My dad is looking to get a program where he can design houses. He normally draws designs for homes, or things he wants to build for people. (He's a carpenter)
But it takes him awhile for it to look really good. I don't know if Adobe photoshop or whatever would be good for what he's looking for. Basically a program that will suit his needs and make his work easier for him at the same time.
Well, all these things require some training, whether using a 3D program, CAD, or drawing program. I don't know if he's good at drawing, or his current techniques for sketching up designs for people. If he's looking to draw stuff by hand, there are free paint/graphic programs (do a google search), or he could even use MS Paint, which is already part of windows. Next level is spend a $100 bucks on a wacom bamboo drawing tablet at best buy, now you can hand draw and sketch on your PC.
CAD/3D There are some programs out there that have to do with home design that might be able to serve his needs without having any extensive knowledge of 3D/CAD. If he wants to get into it without spending money on some of the premium 3D programs, you might want to look into google sketch up, which i believe is free, and then there is a paid premium google sketch up, and this allows some architectural drawing etcetera, people use this program to make buildings to add to google maps / google earth.