I had some SS work done by sheetys, best I've seen yet. (Comparing to work I've had done & seen in HB stores)
The best way to weld SS is to TIG weld as it has a very localised heat so it doesn't buckle the work. This is more important the thinner the material is.
As BigD said sheetys can roll, cut bend etc but you may need to find someone that specialises in SS. Maybe speak to your local HBS - thay may have someone they get stuff done through?