On Vanilla, spawn shops have different rules than SMP and other servers. There are no set plots or pre-built stalls that you rent. The rules for building shops are simple:
Don't build a shop taking up a ridiculous amount of space (does not include height)
Don't build a shop blocking other shops
Don't build a shop on paths
Don't build shops with TNT (believe me, it will blow up eventually)
Don't put casinos in shops (only build those in the gaming district)
No small microshops dotted around the shopping district
As of 1.16, shops DO require payment. These payments will not be expensive and only exist to keep people from creating too many shops cluttering the district. More info on this will be provided with the update. This information is also written in the area under the spawn hill.