An straight forward and easy way for multi-unit dwellings to go solar does not yet exist in the US market. This is because it is quite difficult to Net Meter the use of each unit separately when the building would have a single system on its roof. The question of who gets how much credit for the production of system becomes complicated. There are some companies that are working on solutions for this problem.
Having said that, some folks who do not have the patience to wait for such solutions are creating their home made solutions. This is a cool video that shows how an apartment renter is sustaining his electricity use for many things at his home. It is not necessarily the most aesthetically pleasing look but it certainly does the job.