The best and quickest way to produce a 3d drawing of the walls is to convert all your wall lines to polylines using the mpedit & join commands then using extrude to give you a height to the walls.
Or in 2010 you can use the presspull command.
This will get you started off.
Can you upload a pdf file of the plan and side elevation to give us an idea of the roof line etc. then we can give you some more better directions.
(p.s you need a minimum of 10 posts to upload files)