Help with house design

Hi,
I've created a floor plan using the line function then copied 2
references of it and created a plane for the floor and created an
editable poly and extruded upwards for the walls. The main problem I am
getting though is that when I want to cut in a window or door to the
walls I am only able to do it on the poly face I am looking at. Which
obviously means I then have to align the vertices on both cuts and then
create some poly's for the insides of the window. I am pretty new at
this and wondered whether I was going about it the right way. The house
is a pretty simple layout but I'd like to get it as close to the
original building as possible.
I have also tried using the slice plane tool but find that it is quite
difficult to get the desired lines in it. Perhaps I just need to
practice it a bit more.
Any help would be much appreciated.
Cunning
(Using 3DS Max)