Usually, when enemy cata/ballista is captured it becomes a dead weight as it cannot be used against the enemy (and even cannot be destroyed unless you're a bulder), so i think there should be an option to turn them around (like the flip option when vehicle is on its back). That option probably need some kind of price or condition - like certain amount of people near the vehicle or price of 100-150 wood. The other option is to just give the ability to make wheels again so in can be spinned for a price of about 200 wood or they could be bought in siege/builder shop. Both these methods will probably enable griefing, on purpose or not, but options like that can make game more fun entertaining. Furhermore, what can be more memorable than driving catas from tower after capturing it? If you have any additions/critique plese comment.