Would like to generate a structure and set spawn point for new players automatically

I'm creating a zombie survival world and would like new players (on join) to automatically be given and teleported to their own base. The base will just be a rectangular room with no windows/doors (the only way to get out is to teleport). Any tips for making a procedure that does something like this? The bases can be next to each other in a grid (like plots) since players won't be able to see/get out of the bases anyway. I could also pre-build the bases if necessary, would just need to figure out how to make a list of each base/coords and assign them to new players automatically. 

I thought about installing a Plots mod and just using a command procedure to automatically give each new player their own plot and setting it as their spawn, but I'm really hoping there's a better way to do it.