When you say "each" nation do you mean "all" nations?
I mean do you want me to make one set that you can use for all nations or make each nation their own set?
Wouldnt they unbalance the sieges and if not why didnt Kristoffer made them.
Major siege engine classes I know of:
Trebuchet
Ballista
Catapult
Onagre (although no idea how to draw this one)
Mangonel (also no idea) sp?
Chinese Rockets
Siege Tower
(And if you want) Cannon
Many different versions of Battering Ram (from simple tree trunk to ram on wheels with roof and stilled head)
There where many more but I cant remember them at the moment. The best way to do this would be to take the sprites from Total War games then adjust them for Dom.
I've changed some sprites in the mod but I'll wait for bigger changes to release it.