My shed is going mouldy!

[mini lop1]

ours is leaking somewhere, but dad been on top of it numerous of times checking it and can't find where its leaking in from on the roof, he even put a brand new layer of felt over the top but it still gets very damp, our neighbour says theirs is exactly the same

 

[BB Mommy]

I've got 4 sheds, three of which house bunnies.
All the bunny sheds are fine but the one that houses the bikes and mowers is soaking:?