If you can do the metal fab, then it's a matter of planning, measuring, measuring, measuring (did I say measuring?). . . and then cutting. Tex Smith's book "How to Chop Tops" is worth its weight in gold for a first timer.

Amazon.com: Tex Smith's How to Chop Tops (Hot Rod How to): Books: Leroi Tex Smith,Rich Johnson

O'Toole's book is good also.

Amazon.com: Chopping Tops: Practical Hot Rodder's Guide: Books: Larry O'Toole

You'll learn more in those two books than you will with a hundred questions here - although I'm not discouraging you from asking.