Price for retiling roof? Surrey/Hampshire borders

[jack]

A mate of mine got some guys in to clear the moss off his roof. Turns out it's in really bad condition - felt is leaking in several areas, battens are in poor condition, and various other issues. Some of the rafters are wet but there's no rot yet. It needs to be taken off and redone.

 

It's a medium-sized four bed semi with a simple double-pitched gable roof. I won't tell you the price the guys doing the moss quoted him, but any thoughts on a rough cost for this sort of work (basically remove and replace everything from the rafters up)? Tiles are clay if that helps.

 

Thanks.