Found this stuff on screwfix and its a good price to fix a leaking flat roof.
flexacryl, c £10 a tin with 5 delivery, I got 4 tins and still £5 delivery
If you haven't got a leaking roof right now it won't be much of a deal but if you do you'll realise its priceless. I had water coming through the lights which was a bit of a worry.
It goes on in any weather/conditions, comes in different colours and is a durable long lasting fix - I phoned the manufacturer as I didn't want a short term repair.
Its an instant fix too. Flat roofs are notorious for leaks so hope this helps, I spent ages trying to find the right stuff and I think this is a cracking price to repair a roof. I thought I was looking at a big outlay. Next day delivery as well.
Its instant, you just paint it over the crack and thats it, job done + it will last for years. Similar stuff, ebay for eg is £20 + del.
I didn'tr realise but there are also money off codes too which makes it even cheaper.