How about this, lets say that NCR recently wanted to open up their homeland of V15 back up and needs the help of players to repair it.
At first all you see are some guards and a pathetic excuse of a caravan salesman that sells like junk items. Only the top level is guarded right now as the project just started, so the lower levels are still unguarded as there isn't a priority enough to put guards down there. The reason why NCR posted guards there and prolly Gunther to oversee the project is that NCR wants players in the wastelands to help them rebuild V15.
What i mean is that a player would go to Gunther or someone designated by NCR to give them materials like wood, stones, ores, fibers, electronic parts, metal pieces, ect.
To re-open the first floor everyone would need to donated like 1000 pieces of each of the materials needed.
The first floor would have
-Few rooms open to renting.
-A Doctor
-Some higher tier sellers
-Arena for various styles of fighting.
A plus thing is that the top floor gets better and better with each floor getting upgraded as NCR is taking an even more interest in the place.
Second floor would need something something like 5000 resources of each.
The second floor would have
-More rooms open to renting
-medical crafter machine
-Merc buisness
- even higher tier sellers
-ect
I forgot how many floors there are but each floor would get need even more better and eventually items such as good metals, water chips, MFC, energy weapon add-ons, ect, would be needed to complete the last levels.
The way i see this working is that a lot of players would need to contribute and the lower levels would take time so as not to spoil their effects. Maybe when you donate materials NCR would pay you money, but with a lower amount than if you had sold it to a seller.
For players that didnt contribute resources they wouldnt have access to any of the floors but they can gain access by donating a small percentage of items for each floor. For example based on the first floor example they would have to pay 5 or 10 resources of 3 items of their choosing (ores, metal pieces, rocks) So that the lowers levels aren't spammed with characters that would take the rooms for people in the lower levels and other benifits.