Finland never built the Buffalo. They were taken from USA by ship to Norway and assembled at SAAB in Sweden. The Buffalo was bought just because it was the only somewhat current type that was available, and orders were to get something, NOW. Wildcat production had only just started. All Seversky EP-1 production was going to Sweden.
As far as I can tell, the Humu fuselage is metal, and the wing is wooden. The fuselage looks riveted in a Wikipedia photo. Initially, the Shvetsov M-63 engine was found lacking in power, and not very reliable. Later on, manuals for it became available and proper tuning made the engine stronger than the original Cyclone.
https://en.wikipedia.org/wiki/VL_HumuThe Finnish Air Force Museum has the one prototype, but looks like it is in storage now. I remember seeing it at an airshow in Tampere, near the former VL site, in late 70s (?), together with the Pyörremyrsky prototype.