Surely the majority of the thing is just a big shed?
You can almost certainly get away without putting side walls on it (the point of the roof would be to keep the rain off the tools. Which makes it a better gaming piece as well :-)
So it's just a base, some verticals, roof struts, roof.
The inside mechanicals is the tricky part, but they're either available commercially in S scale ( Frontline Wargaming makes link ) or also reasonably easy to scratch build.
For the Old West era, it would a steam powered blade -- so that's a boiler, chimney, a small complicated bit and a band powering the sawblade
A broken clock ought to provide a large gearwheel to pass as the blade and then you just need a wooden tray around it.
One end of the building is full of reasonably straight twigs passing for logs, the other end full of stacked balsa strips.
finds bases at the dollar store!
