I've rented out my top floor of my house for a one time payment of one million gil. My tenant got 50 slots, full craftstations, full gardening, full privilege to remodel the walls, flooring, ceiling light, windows, armoire, company box, immediate access to the marketboard so they didn't have to pay tax on Lominsa purchases and even chocobo stables.

Granted they could have paid 300k for a fc room since you also get 50 slots, this would have been the cheaper way to go for them, but I find that fc rooms have a very limiting design flow, where as the upstairs of a medium plot is more open and allows for more customization.