1. I've been to rooftop area outside Noble House restaurant (UIC Building)... not sure if it's open all the time or purely because of the wedding.
2. Marina Bay Sands meet your criteria? Marina Barrage kite flying area (not very high but u can shoot from below)?
3. Pinnacle @ Duxton (need to pay)
4. Vivo city rooftop (again, not very high).
5. A quick Google gave me the following: The Helipad (
http://helipad.com.sg). Lantern Rooftop Bar @Fullerton, and a few more at
http://sg.promotion.yahoo.com/weekend-edition/nightlife/post/nightlife/27/rooftop-hangouts.html. Also
http://flickr.com/photos/adforce1/4227686279/
Probably need to pay for most of them except the last one (Hong Leong Bldg carpark level 8 ), not sure if professional photography allowed.