Ok, quick question, when you say "Make units walk on buildings" do you mean like walk on TOP of the building? Like on the roof or something? Because if you do, simply make a new doodad based on the bridge model and change the model file to whatever you want. After this, get rid of all the pathing map thing (set it to None) Then use pathing blockers to block where units cant go on the building (You need to raise the blockers height, otherwise it may not work) Anyways, good luck to you.