Spoiler
Playing through Vault 11 in New Vegas made me think, "I just tore though a whole vault of nothing but giant mantises and rats, if I wanted, I could move a bunch of refugees, legionaries or NCR troopers in this dump and make it a functioning community."
So if this thought came to me while playing New Vegas, how about investing in a plot of land (like buying a house, only more expensive) along a very good potential trade route and paying an architect to construct an inn, some shops and a few houses, you come by every few days and collect your towns revenue. You hire an assistant who you can tell to set taxes (which will determine how much travelers will spend in town and how much you get off of each transaction), arrange upgrades in the quality of goods that can be purchased from shops and other things.
Another thing that you can do with a building footprint is decide if a Mage's guildhall, Fighter's guildhall or a Thieves Guild corner-club will be built here, at which point the place would pay taxes on jobs being taken (in the case of the former two) or some hush money for allowing the Thieves Guild to operate out of the corner club. Various merchants associated to your choice would appear in the building that you chose to build.
This could obviously expanded to include a LOT of things, but since it's late, I'll cut off here and add in details at about 11 local tomorrow.