In my opinion it is more realistic now. If you need to build something in real life you can't do it over a tree or over a lot of rocks, but you can easily remove a sheep's corpse to do it there. Edit: It seems that if some units are atacking they aren't considered as obstacles for building and they won't move from the placement of the new structure, which makes the building process impossible just like in the case of the sheeps. (tested with ranged cavalry).