David, I am responding so you know you have made human contact.
I have only the three Bay Atlas O Roundhouse, but I had to cut/grind away some of the front apron to properly contact my Millhouse Studio Z 22" Motorized Turntable. My added table area for the turntable does not allow for a bigger Roundhouse. I will have outside stubs from the turntable for parking engines. The Roundhouse is for repair purposes only.
Another Roundhouse Kit will give you more Bays, but you may have to cut the front apron to fit around whatever turntable you use. I used Woodland Scenics plug and play lighting inside the Roundhouse. I have red LEDs above the doors to indicate if power is ON for that track. I extended the middle Bay back though the rear wall for my Big Boy and Challengers.
There is a picture of the turntable upside-down to protect the painted Turntable well paint. I am still building. I may never finish.
Sincerely, John Rowlen
