Painting question, should i paint parts separate or together...?

[tripleblack]

I was wondering if i should put my truck together and then paint it or should i take each part to the paint shop and then bolt them together. I am going to weld on my rollpan so my bed has to be put together before i paint that so but as far as the doors and front fenders, hood, cab and everything else besides the bed, what should i do. Maybe if someone on the board has been through welding a rollpan and could give me some suggestions from experience. By the way, the reason i have no problem painting all the parts separate is because my whole truck is appart and have preatty much all new reproduction sheetmetal. Thanks.