Ok, lets assume that PW will let you do what you wish.
As far as freesat (as against freeview) is concerned all you really need is a Dish of at least 1.2m, an LNB (the little block opposite the dish) and a satelite receiver (a regular sky box will do). You should (after some messing around with Dish alignment etc) be able to pick up most free-to-air channels. However, to view certain channels (like channel 4, 5, fiver etc) you will need a viewing card registered in the UK (about £20). They are still free to air channels but you will need the card.
If I were doing this for one of the appartments (ground and first floor type) then I would get together as a group and buy the biggest dish (say 2m) I could afford and one that wasn't going to take over the whole solarium. Then buy a dual or quad LNB. This will allow you to take two or four feeds from the one dish, which would give you one feed for each appartment or recever.
Anyway, don't want to bog the thread down, there are local companies that can do this, but I think the only hurdle will be PW and their regulations on what can be put up (plus the owner of the roof top property). The other thing is that any dish over 1.0m would normally have to be floor mounted.
Regards,
Steve.