High rise building? What the hell else should a building manager be using that gigantic, flat roof for? (Other than leasing space to a cell-phone antenna, of course) You don't have direct control over this, so I suggest looking for it as a feature the next time you move, if it's that important to you.
And how's that roof which is, say, 10 times the size of a house's roof, going to supply power for hundreds of times as many people?
Sure, some costs are saved (e.g. heating and, probably to a lesser extent, cooling) by the higher density, but you're also crazy if you think that the 'available power:used power' ratio is comparable between apt buildings more than a few stories and residential homes.
(I'm not saying that there shouldn't be solar cells on the roofs of apts, at least in lieu of a nice garden or something like that which you occasionally see, but I seriously doubt you'd be able to create a net-zero, tall apt building unless it's filled with people who are completely dedicated to very very low consumption.)