My swingout tire is on the drivers side as it seemed to block visibility less. This means my ladder to reach the rest of the roof rack was on my passengers side, which meant my tent had to be on my driver's side.
That said if I didn't have a lengthwise half roof tent, but a square tent, I'd probably have it open up to the rear of the car if at all possible. Give me more of a "roof" over my tailgate kitchen area.
Cheers,
JFS III
EDIT: Pay no attention to my avatar picture, that was taken a long time ago when I opened it up to be entirely over the roof. Now I store stuff on the other half of the roof.