These are just general suggestions for areas to look at.
Lots of nice places around Winchcombe just north of Cheltenham in the chalk Downs. Lovely rolling hills etc. Loads of stuff around Broadway in the Cotswolds may be suitable, especially at the top of Broadway Hill. Check out Streetmap etc for more detail.
More specifically - A few miles south of Cheltenham there's a fantastic view from Birdlip Hill looking west over Gloucester. It's one I must get around to doing myself one day.