Literally just buildings you're allowed to build inside of. Kilns, fireplaces, smelters, etc.
Both versions would have an upstairs area
Maybe the large one would have a basement as well.
Large double doors in the front (and back?) of the building, big enough to fit a cart through (this is purely cosmetic, I know carts can go through normal house doors)
Part of the construction allows for placement of signage outside that can be given an icon like a display sign can, so you could put a metal bar on the sign for your blacksmith shop, some linen on the sign for your tailor shop, etc. or even a sketchbook page if you're feeling really fancy.
Also, on the side of the building there should be several "chutes" or "trap doors" or something similar graphically that allow the player to bring a wheelbarrow up to the wall and dump a stockpile, and that stockpile appears on the other side of the wall. If the player is inside, the stockpile appears outside. If the player is outside, the stockpile appears inside. Maybe make 4 of them, 2 inbound and 2 outbound or something. The idea is that you should be able to easily transfer bulk goods from inside and outside without having to deal with the hassle of moving a wheelbarrow through a building door. Make these areas inaccessible to the player and animals to avoid weird collision/hitbox troubles. Loading and unloading zones ONLY!
Might also be a nice touch that if there's something on fire inside (fireplace, oven, smelter, etc) the chimney on the top of the building smokes
