For solar I'd prefer to have two wires, positive and negative from the roof, all the way to where you are going to have the solar charge controller placed (close to the battery). I believe that the common thing is of one wire, positive for the solar, and then using the camper frame as the negative The roof has a positive and a negative wire for the ceiling lights and any roof mounted fan(s) to get down from the top to the main camper frame, i.e., past the pop-up soft sides. However, I'd like to have the solar to have both a dedicated positive and negative wire.
If you have any special components that you want ATC to install, they will do it for you. Things like a special vinyl floor covering design, perhaps a different flame proof headliner, specific interior lights, or a roof fan that you can buy at your own price.
When I placed my order I brought to ATC my left over bathroom remodel vinyl flooring, I purchased some marine grade flame proof headliner material, some marine LED ceiling lights and I went to a RV place and purchased the fantastic fan when it was on sale. if you're not close to ATC, then you could ship them your special items, if that is cost effective.
Is this for a shell (building the interior yourself) or an ATC built interior?