New to blender - Texturing problem

Hi,
I’ve just started to try blender (my 1st 3d program anyway) and have been using several tutorials that are available.
One of my first attempts was trying to model an house using booleans but cam across one problem. when I try to apply color it is applied to the inside walls and not the outside ones.
That a look at the picture bellow:
http://img144.imageshack.us/img144/1787/renderte4.jpg
Any help is welcome.
Best regards,
Jorge Antunes

you have to tell Blender what is “outside”, and that is called the Normals. Right now, Blender thinks the left wall should be on the right, so that the one side is facing outward. Normal is a geometry term meaning at a right angle away from a surface.

For the walls that are flipped, In Edit mode, select those faces (walls) and Mesh->Normals->Recalculate Outside.