In the works for about 10 years, the Oklahoma Model Railroad Association now (as of Nov 2018) has their own 2 floor building just east of the BNSF mainline near NE 44th and Sewell Ave (north of the capitol). The building has almost 12,000 square feet, with different gauge (size) layouts on each floor. They have HO and O/On3 scale tracks.
They have been operating a modular HO scale layout with a three track mainline approximately 9 scale miles long, with multiple industrial sidings.
Club dues are $120 per year.
I was there on a Saturday morning, and members were there working on the layouts. The web site shows it to be open Sunday from 1-4 pm.