It's always best to design your unit mix based on local market conditions to begin with - this is one of the advantages of a good feasiblity study. As a site planner I have seen more call for 20x10 units with two doors versus regular 10x20's. If market conditions change, the 20x10 unit can easily be changed to two 10x10's by adding the divider wall. Smaller units could be designed the same way - like including 10x5's with two doors instead of 5x10's. Of course, the multiple doors could get expensive if the need to divide the units never occurs. A phased project is probably a better way to meet changing market demands. What you learn in the lease-up of the first phase of buildings can incorporated into the design of Phase II.

Steve