Hi! The group 'SolarWashington' can probably hook you up with some great urban sites, like at Ballard Library. They also do a tour every year and you may be able to check out who has hosted on those tours.
The roof! I've totally had so many thoughts about that, how all sites need to do Something with the roof.
Solar Electric
Solar
Hot Water Rainwater for garden
Rainwater for toilets
Greenroof
Rooftop Gardens
I think about in terms of how much time/money the residents under the roof can put into it. And some roofs will be able to do certain things, some can do multiple.
I see rainwater being easiest time wise, and rooftop gardens the most. And then for money I see again rainwater for garden easiest, all things garden the next, greenroof (depending on structure capabilties) and hot
water in the same camp, and solar panels as the most expensive input. But then, you get out what you put in
For an apartment that would let you on the roof the rooftop garden, and water collection, has so many community assets that would tag onto it. I'd think that would be the easiest unless folks are already organized
enough to invest in panels.
An aside (both solar hot water and greenroofs Can be done on the cheap with correctly salvaged material. Just so you know it's possible, may not be easier though).