Set it in place and see how it looks.
underworld
Not sure if this may help but what about using an S gauge building for the roundhouse and an H.O. turntable as that is what I think the On30 track is.
S Helper may have something in S gauge.
Lee F.
You could run a track off the main board on to a separte board just big enough for a round house and turn table. This may help with not over crowding your layout.
Bowser makes turn tables in a couple sizes.
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