Adam,
As far as I understand the situation, there are two types of solar panel models. The first, which you are referring to, is when the property owner purchases the solar panels and sells the electricity back to the tenants, presumably at a markup. Leasing space is a different approach in that the utility company is responsible for the installation and maintenance of the panels; in exchange for that arrangement, the electricity goes directly into the grid and is sold by the energy company itself. The property owner receives no electricity from the exchange; instead, s/he gets rent for the surface area of the roof.
I am starting to get the impression that leasing roof space in our market is not an available option. I'm guessing the 300+ overcast days a year make solar a less attractive investment.
I like your idea of renting the building as multiple units. I'm pretty sure I can get one unit per tenant but that is not enough to cover the costs of repairs. As you guessed, the layout is not quite conducive to supporting non-resident access as the tenants will block the driveway to the structure.