Why not choose over-sized windows like here:
I have never seen this before but what a nice way to a) let light in and b) create more space in the room. Not sure Harringay council would let us do that where we are, but why not give it a go?
Tip*1: If you decide to go with roof windows, try to pick the biggest ones you can and remember not to put them too high so the light does fill as much space as possible.
Tip*2: Amongst other roof products - like roof ladders, solar panels, roofing membranes etc. - Fakro offers a wide range of windows from basic roof windows to more eccentric products like balcony windows. If you have used any of their products, please make yourself known.
27/07/2011 Update
My absolute favorite so far, seen on Pure Kitchen:
