Gingerbread House

I’m making a gingerbread house for Christmas. I have the gingerbread boards finished, and I’m trying to use the boolean modifier to cut out a door. But it keeps saying that both meshes need to be closed. Could this be happening because the walls were extruded from a plane? How would I solve this?

I would suggest making your “cutouts” in the Plane before extruding them. Use the knife tool to make your cuts in the Plane. Then, switch to Face Select mode and delete the faces that represent any openings in the wall. Then, extrude the Plane. This will also keep the vertex count to a minimum.

A faster and simpler way, but resulting in many more vertices, is to subdivide the Plane and delete the faces that make up any desired openings. Then, do your extruding.

Using booleans may present some topology problems later on.

Thank you. I decided to just outline the door in frosting. Next question: How can i make particle snowflakes accumulate on the roof?

EDIT: Okay, I have most of it done. What do you think?
http://www.winsley.org/images/gingerbread.jpg