Bodywork help?

It appears it was to good to be true and my car has some visual rust that I didnt catch when I purchased it. Now my question is how would a professional body shop go about fixin it the proper way. The rust is located on the roof where it meets with the trunk lid. Its not directly on top of the roof its just below the lip of where the roof stops and goes just short of half way across the passenger side. and its got a small gap seperating the roof in some parts to I guess the bottom side of the roof where its hollow if that makes any sense. I don't have a digital camera or I would take pics. I'm just lookin to find the proper way to get it fixed is it something a body shop would bondo? or would they cut the rust area out and weld a new peice of sheet metal to the rusted area and grind it down for a smooth edge? Any help would be greatly appreciated thanks fellas.

Thanks man I wish it was surface rust but I should have mentioned it has ate all the way through thats why i was askin about welding another peice in the area after cutting out the rust. I would rather not use bondo i like to do things right the first time so I dont hafta go back to them later but I'm no specialist in the body work field. I'd really hate to remove the whole roof it seems like alot of work plus my interior is near flawless.