Alpine Division Scale Models.
What is Alpine Division Scale Models?
ADSM makes HO scale buildings that will fit perfectly with 18mm figures from Blue Moon. From their website: "Our product line is made from durable top quality laser-cut matboard and basswood; the same matboard that is used in the framing of your pictures and pieces of art. The ease of construction and overall fun that these kits provide make them an ideal project for new and old modelers alike. Wood glue is used in the assembly, and plastic doors and windows are provided with most kits. Using quality model paints will produce very fine looking models. Most of the kits have roof detail, some have signs and lighting, and some have interior detail."
I haven't built any of kits yet, but I did build some way back in the 1970s and 1980s when they were originally sold by E. Suydam. I built the Modern Yard Control Tower, Purina Feed Mill, Packing House, and others I vaguely remember. These were easy to build, lightweight, looked good, and were very sturdy--all good qualities for gaming buildings. I assume these kits are even better now. I hope they eventually release the entire, large Suydam catalog.
If you are interested in gaming Westerns using 18mm figures from Blue Moon, Alpine Division Scale Models makes over a dozen inexpensive ($12 or so for most of them) HO scale Western buildings under their "Old Town" section. Poke around their website for more buildings if you plan on gaming Blue Moon's upcoming 18mm gangsters or anything else set in 20th century America. I thought I'd pass along the suggestion.