It's also like how yar not allow'd to build snowmen RIGHT in front of a house. I try'd to block the enterance of The Roost to see what happens, and it fail'd badly. As I set the body snowball in the space where door would open and spawn the character back into the town, I push'd the head snowball into it to complete the snow but wound up crushin' the body part and destory'd it.
I would guess that snowmen placement and floor types might have similar "flags" and such that the game notes to dis/allow some actions to happen.