Well, it has been about a week since I added anything so I thought I would post an update.
Once I got the turntable in the hole and the roundhouse scoped out, I realized I still had a lot of heavy lifting to do (cutting holes, using glues, laying track, completing fascia, etc.) and I did not what to do that after fine tuning the turntable. So I have spent the last week cutting the holes for the inspection pits under the roundhouse (per Trainiac77), cutting the inspection pits for the diesel area, completing the fascia, laying roadbed, track and turnouts in the area around this area and test fitting structures for the area. I also had to build ramps to lower two approach tracks from roadbed to tabletop to be at the correct height when they reach the TT and I built an upramp for the gondolas that service the cinder tower, coal tower and sand area. In the process I reduced the roundhouse to 5 stalls, added a track for the second coal tower chute (I had forgotten about), assembled the sanding facility so I could make sure it would fit and I am just finishing kitbaching the diesel sanding rack from 24" to under 12". The upshot is that I have all the roadbed in and all except about 10' of the track in. Also, I found that the screws that come with the Walthers 130' TT are a bit short since I used wood that is slightly over 1/2" thick so I had to send off for some longer ones. When they arrive I should be ready to secure the TT and start adding the tracks that lead to it. Oh, yes, I also decided to rotate the TT 90 degrees to avoid any problems with the "no track here" areas which were a bit close to one of my intended approach tracks. Attached are a couple of photos of the progress. More later.