Going to start locally with two of Peckham's finest...
There's a rooftop cinema with some amazing views of London. I <3 Bussey, especially in Summer.
Do I really need to tell you how great this bar on top od a multi storey carpark in Peckham is? Really? Ok, it's bloody lovely and opens next Friday. I will be face down in some vegan kimchee (the menu's great!)so come say hi.
Roof Garden - Southbank
It's guaranteed you'll find yourself on the Southbank at some point in the summer, so do check out the roof garden on top of Queen Elizabeth Hall. It's no smoking but has BYOB potential. Oh and it's been designed by the folks behind the Eden Project too so it's very pretty indeed and, of course, the views are outstanding.
Netil House 360
The roof of this abandoned college transformed into a thriving creative community is pretty special. They have some cracking BBQ's and you can also make use of the wifi and work from there. Tip: cocktails whilst working are always a good idea.
Around Hoxton and Haggerston you'll find a cluster of pubs with good roof terraces. My favourite's are The Fox and The Red Lion. If you venture a bit further into De Beauvoir town then The Talbot has a nice expansive terrace/balcony bit.
A slightly lesser known spot than other East End sky grazers but an absolute joy once you've found it. If good Italian food in the sun's your bag (whose isn't it?) then Lardo's London Fields based Italian "Rosticceria" will be your summer oasis. Tip: it's on the roof of the hothouse and by be reached from Martello Street.
The Queen of Hoxton
Not my favourite bar to be honest but once the wigwam comes of it's rooftop then the trek up all the stairs for those views and a summery vibe is often worth it despite the sorry drinks selection. The decor is a treat to behold. They also have some screenings and good events, just avoid the oompah loompah coloured crowds on a Saturday night.
Dalston Roof Park
More astro turf and kitschness can be found a little further north. I've talked about this spot before and will continue to because it's a multi-pack of fun. Tucked away on a Dalston roof top above the sirens and irony below you can enjoy a brunch, cocktail or film - that's if you don't mind queuing mind.
Even though I used to live in North London it isn't really my stomping ground. The Beach at The Roundhouse in Camden is quite nice and The Driver in Kings Cross has a nice, if not slightly bizarre roof terrace.
I rarely go out in West London but The Kensington Roof Gardens are kinda special as long as the sun doesn't reflect off the coloured chinos and blind you.
As per I can't be everwhere so have probs missed some. Please let me know and I will drag myself over there and force down another cocktail. Roof terrace suggestions outside of London are very welcome!