I have this flat roof which has started to think it is a garden, see pictures. It is about 30 or so years old, size 2m by 4m, with easy access by ladder. The little stones on top are not glued down I could brush them up and clean them in a bucket of water. The roof is North facing and shaded by the rest of the house, it gets very little sun and even then only in summer when the sun is low in the sky and lost its ferocity, plus I am in Scotland so the isn't very much sun anyway. Painters have been up on the roof occasionally, they put a board down for their ladders.
What needs done? Will it need a pro or can I do it? If it needs a pro roughly what might it cost?