Hey I take offense at that. If you knew anything about 3d rendering programs then you wouldn't be asking this question. You didn't ask for anything specific, you just asked for a program to convert pencil and paper to web.
For simple drawings you can use Visio, Photoshop, or any of a bunch of drawing programs. It kind of depends on what you have access to or what you want to spend if you don't have access.
For converting to 3d perhaps someone that knows more than I do about that will post an answer. Now that we know your interested in 3d rendering.