You may want to proceed slowly building around the roundhouse with the space you have available. You may wind up with a steam engine servicing display layout, unless that is your goal.
Having more than one TT which was a necessity due to my layout's theme it became apparent I had to compress the engine service facilities for an overall visual balance.
A 1930 aerial view a PRR facility gave me some direction. In a crowded urban setting the ready engines were stored in a linear fashion leading away from the TT instead of the traditional TT radial fashion. The take away is that there is much more available aisle space and an 18 stall round house looking for a new home.
