You could try a Fractal Design Define R5, should be able to find one under £100 with a bit of shopping around. I'm very happy with mine. Not sure how well suited it is to water cooling but, the front drive cages can all be removed, the lid is long enough for 3 14cm fans and, it's "only" 232mm wide.
What he said, Fractal are awesome for the price, some other ones well worth a look in that sub £100 price range: Lian Li PC-O11 Air Phanteks Enthoo Pro M Silverstone RL06 Pro Be quiet Pure Base 600 (in no particular order)
For watercooling or just for better airflow in general, I'd go with a meshify c. It's also quite compact at 409 x 217 x 453mm, but you can still fit a 360 rad in the front and a 240 in the roof. And it's only £80, you can get one with darker tinted glass for a bit more stealth, or a windowless version if you don't care to see inside. But if you're watercooling why wouldn't you?
Yeh kind of. The meshify c came first, about 2 years ago I think. the meshify s2 came later as a meshed version of the define s2 for better airflow.
Ah sorry. The define, not meshify. The define s will be heavily reduced to shift old stock since there's the new model (s2) out. The define cases won't have as good airflow as the meshify, particularly for radiators, so you'd need to run your fans at a higher speed to compensate. If noise isn't an issue for you then that's not to much of a problem, but something to be aware of when choosing your fans.
