The information presented here was compiled with painstaking effort by the author, and should not be re-posted in whole or in part elsewhere without the author's permission.

-Wood can be purchased in Tir Na Nog, Innis Cathaig, and at any Merchant Keep.
-Ferrite Winding Cranks can be purchased at Innis Carthaig and at any Merchant Keep.
-Ammo Buckets can only be purchased at Merchant Keeps.
-Counterweights can only be purchased at Merchant Keeps.
-Pivots can only be purchased at Merchant Keeps.
-Tanned Arm Cushions can only be purchased at Merchant Keeps.
-Catapult Stones can only be purchased at Merchant Keeps, and are not stackable or craftable.

Example: Garek is a L50 warden with 168 strength. Self-buffed (w/ L50 strength buff, +50 strength) his strength is 218. Check your encumberance, self-buffed, to know how much you can carry. Keep in mind your armor and weapons count against your encumberance too, so be sure to look at your encumberance and not only your strength. Also remember that Realm abilities like Lifter can greater enhance your carrying capacity (+20% encumberance per level of skill). With 211 str the max encumberance is 210, but Garek has Lifter I, so his max encumberance is 261. This character carries approximately 50 pounds of equipment (tools, weapons, armor, arrows, etc.) so he can carry 211 lbs of equipment. Although Garek's strength is much higher with a druid's strength/constitution buff, he does not carry more than 211 lbs of siege equipment. The reason for this is, if someone is strength buffed and their buffer disconnects, they will be overloaded, and likely unable to move. If you come into contact with the enemy while moving to your objective, and the strength buffer is killed, overloaded party members will become rooted by their encumberance, and easy pray to enemy troops. Wardens, Bards, and Druids are ideal choices for carrying siege equipment for their self-buffed capacity, with Heroes, Blademasters, and Champions being a close second for their raw strength. Many members of these classes are also often Firbolgs, which gives them an even greater weight capacity.
 

Allocating parts for one catapult across four carriers should look something like:
Engineer/Gunner: Tanned Arm Cushion + 20 Catapult Stones = 130 lbs.
Carrier 1: Ferrite Winding Crank + Pivot  = 97 lbs.
Carrier 2: 100 Wooden Boards + Ammo Bucket +Counterweight = 135 lbs.
Carrier 3: 500 Wooden Boards = 125 lbs.

Make sure you have a sewing kit, smithing hammer, and planing tool on you when attempting to build any siege weapon!

To physically emplace a catapult, you need to keep in mind the areas you want to bombard. Keep in mind that the ballista is an area effect weapon, so in RvR you will want to avoid hitting NPC spawns. You need to be particularly mindful of the minimum range of the ballista. Because it uses indirect fire, it does not require line of sight, but it uses the physics of a parabolic arc when firing, so your target must be a set range away to be fired on. The minimum range of a ballista is approximately 1500 units, and the maximum range is approximately 3500 units. Using /loc, you can estimate these distances. In defending a keep, you will need to place the catapult in the lord's tower or along the back wall in order to deliver fire on the gates. In the offense catapults can be used to deliver firepower on a defended keep, but you will need an accurate ground target. Do not build the catapult too close to the keep being attacked or it will be useless, and expect to have heavy counterbattery fire delivered on you if you deploy a weapon in a siege - it is very easy to target siege weapons outside the keep, but very hard to attack them inside.

The equipment carriers pass the engineer the full list of components once the engineer is standing in the spot the weapon needs to be built. The weight of all the components will overload the engineer to the point that he will be unable to move at all. Be mindful of this if the engineer is killed before construction is complete! If the engineer needs ressurecting before he has built the weapon, the resser needs to stand exactly where the engineer died, so that the engineer will be in the correct spot for construction. If you ressurect the engineer 50 feet away from where he died, he will not be able to walk to the correct spot, and all the equipment on him will need to be offloaded so he can move, creating a waste of critical time.
 

Now use the key indicated, in this case F10, to set your ground target's location. Press and hold F10, and use the arrow keys to move the pulsing targeting cursor across the ground. The cursor always starts directly under your character, then moves depending on the cursor movements you make. Once it is set, it will remain at the position you moved it to until you log off or manually move it again. When you let go of the F10 key, it plants your target at that spot, and prints out the grid coordinates of the cursor's current location.

There are two things which make ground targeting very useful. The first is that the cursor does not move relative to you, so you can run to the front of a keep, place a ground target with precision visually, then return to your catapult and aim at the new target. The second useful feature is the fact that even if you cannot see the cursor's position as a result of visual obstructions (e.g. you are in a keep's courtyard, and the cursor is in front of the keep) you can still use the coordinates to precisely place your ground target.

If you know you are going to defend a keep with a catapult, I strongly recommend going outside of the keep at some time before the siege begins, and mapping the coordinates of a few spots. Spots you'd target would be the outer gate, and a few areas where you think enemy casters/healers may congregate. Assassin climb points are also a good target to map, because the AE fire will break their stealth and not allow them to Critical Strike people inside the keep on the walls as easily. Write these grids down on a sheet of paper, so you can use them during the defense, and remember that they won't ever change, so you can keep that note safe and use it the next time you defend the same keep, without re-mapping the locations.

It's important to note one thing about locations used by catapults. They use a 6-digit number, based on an absolute grid for the region, whereas the /loc command gives a 5-digit reading in a region. For this reason you need to map your target reference points using the ground target, and not by simply using /loc. I do not know enough about the relation between the two coordinate systems to present a conversion between them.

At the spot the catapult stone lands, players can momentarily see a bag appear on the ground labeled "catapult stone". If you see one of these bags, you know that you are taking catapult fire and need to react to counter the effectiveness of the enemy's fire.

You can click any button in the sequence continuously until the catapult competes that step; although the timer bar resets, it does not restart the 5 or 30 second requirement. As soon as you have clicked "Fire", immediately click "Arm" again. The trick to efficient catapult operation is to focus on what you are doing. The display can be somewhat misleading, because after you have fired the catapult, the status bar begins filling again on its own, even before "Arm" is selected. However, you cannot fire the catapult again without arming and loading it first, even if the status bar completely refills! If you wait for the bar to refill on it's own after completing a fire, it will prompt you with a dialog of the sort "this weapon must be armed first", and hitting "Arm" will re-start the timer. Don't fall into this mistake - your troops are counting on you to deliver as much damage as possible as quickly as possible! Always re-arm the catapult as soon as you've fired it, since that is the longest sequence, and try and deliver rounds onto the enemy as quickly as possibly, since each round requires a minimum of 40 seconds to deliver. 

Macro 1 - Siegecraft menu Trebuchet icon
Macro 2 - /control release
Macro 3 - /control
Macro 4 - /aim
Macro 5 - /arm
Macro 6 - /load
Macro 7 - /fire
Macro 8 - /repair

Now for the construction:
Move to where you want the catapult emplaced, and get the parts.
Macro 1 (builds the catapult)
Target the catapult
Macro 2
Macro 3
now set up your ground target
Macro 4
Macro 5
Drop a catapult stone onto the weapon
Macro 6
Macro 7
Macro 5
Drop a catapult stone onto the weapon
Macro 6
Macro 7

And if the catapult requires repairs,
Target the catapult
Macro 8

It is essential that you watch the catapult's health bar to avoid having it decay before you are done. Catapults decay two different ways:
1) Slowly they decay naturally on a 15 minute timer.
2) Any enemy spell or melee damage also removes hit points from the catapult, particularly enemy bombardment fire from a catapult or ballista.

Presently siege weapon repairs only check the repairer's Woodworking skill using a pass/ fail skill check. If successful, you will repair the catapult's hit points to full. These repairs cost no resources, and do not require any wood or other material to attempt. If you fail your repair attempt, simply try again.