Keep your two canopy runs a good 12" or 18" from the outer wall. This way you can access plants from both sides. It will reduce your pathway width unless you instead build your shed 14' wide. A narrow pathway would give some overlap from the lighting on each side too. Also your wall mounted oscillating fans won't be banging into your lighting array as they move back and fourth.
The plants right up against the wall will never get the same attention as the ones along the pathway. Yeah sure you can reach through to the other side but your limiting yourself if employing a 5' net trellis and a sea of green. Really hard to maintain plants on the far side if the first layer of net wants to be under 24" from the floor. May as well build it to suit multiple growing styles.
If your using flood tables to discharge your run off that's (2) 8' tables on each side leaving you 8' for reservoir etc. Make it 30' long and fit 24 running feet of planting space on each side leaving 6' imo which is enough for reservoir etc. That's alot of additional lbs for that extra 6' in length.
Consider though if cooling w a mini split and one head unit the rectangular space will be a few degrees dif at the opposite end of the room unless you rig up two head units (ideal) imo one on each end.
Just my 2¢