Modifier Problem

Hi all! I’m a beginner in “art of Blender”:slight_smile: and I have a little problem. I tried to make a house but though it was maded from a single object (a mesh plane), the final object (house) appear with two color, with two tint of grey.

The problem is, when I tried to make the windows (with boolean modifier), it works just in the side of light grey. In the side of dark grey, the modifier works bugged and I don’t know why.

I bring up, the house was maded from a SINGLE OBJECT.

I put a video with my problem and I hope that is seen.:smiley:

Thanks and sorry for my bad english!!!

The Video:

The Video:

Please supply a link to your .blend file.
Ensure your face normals are all consistent
Remove any faces inside your mesh or double vertices (select all and W / remove doubles)
Select all vertices and Ctrl+N to recalculate normals
Flip selected faces with W / Flip Normals