I have a shed covered with tongue-and-groove cladding, which I've
repainted on the outside since it was built.

The roof is the same material but covered with roofing felt. I'd like
to make the roof last a long time and I happen to have some bitumen
paint lying around --- would putting a few coats of this on the
roofing felt every few years be a good way of extending its
durability?

Thanks,
Adam