The BN (ex-NP) roundhouse in Pasco was still in use as a diesel shop, although only for minor repairs, through the 70s. It's gone now. As of the latest Google satellite images the turntable is still there, and in use. So, especially if you're freelancing, you could still have both. A roundhouse is fine for diesel service, especially for a small railroad, and reusing it is cheaper than building a new engine house.
