Question about Full Frame

[johnm]

I am building a full frame for my trans am, just finishing up the design process. I have a question to those who either have built a full frame car, or have had some experience. Would I be better off welding the frame to the rockers and having the car as one big unit, then bulding the floor pan ontop of that, or making the frame bolt under the unibody similar to what it did from the factory, still using a new sheetmetal floor pan, but having the frame removable?

What do you think, and thanks in advance.

John