I am a complete beginner when it comes to 3d modeling and have just started to use Blender version 2.70a
I have been following this tutorial step by step from the beginning: http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Beginner_Tutorials/Print_version#Improving_Your_House
Everything has gone really well up to module 20 "Improving Your House" where I have come up against a problem: I get borders in the between some of the windows and the doors when I do the extrusion, as shown in the image below:
They also show in the final render.
I don't know how to get rid of them.