I'm getting an extreme real time strategy game vibe from this. It reminds me of games like starcraft (especially starcraft.), and warhammer 40K that I played about 12 years ago.
I'm assuming the reason the Rotcere hayrack is planned to be 96 hours to build because it reduces time needed to make other buildings.
Building time suggestions
I'd like to able to upgrade this building for more reduced building time or I'd suggest allowing people to build multiple Rotcere hayracks. I'm thinking up to 4 so it's capped at -40% building time (because I think 40% is a balanced amount). 40% would reduce 96 hours to 57 hours if there's another building that takes that long, and the buildings that take 4 hours would take 2 hrs 20 minutes to build.
Well anyway I really like this vibe I'm getting from reading this. I like working for things, and building up things so this sounds really fun.