Thanks for the feedback, Alex Jenyon. Perspective isn't absolutely my strongest area, but I understand the principles reasonably well. I agree that the perspective on the haunted mansion piece is way off. The main problem is where the front facade meets the earth--that line is bent upwards where the portico is. That was an early mistake that I've mostly corrected by now. (The version I posted earlier is by no means the final painting.) There are also perspective problems with the floor of the second-story verandas; I have those lines basically running parallel to the second-story roofline, which is incorrect. That second-story floor is supposed to be just slightly above the eye level. That mistake is going to be more difficult to correct, but it's necessary. As I look over my original pencil sketch, I see neither of these problems. Indeed, the perspective is almost perfect. I'm not sure why I flubbed so badly when I did the digital paint-over.
mmm well if he's looking for a 3D design then yes 3dMax, Alias etc. But if you want to do layouts of a building and the dimensions and all in 2D, then i'd recommend Adobe Illustrator, i do all my 2D technical drawings on that.