Can I do my roofing work myself, or should I hire a contractor?

It depends on many things. If you have done the job before, or helped someone, it's a maybe. Still, if it has been leaking, there may be further damage that you aren't prepared or able to deal with. If that's a possibility, get a couple of bids and go with a contractor.

Brian herewith endorse your enterprise
Elect windless day to do the tarpaper

Depending on how long it's been leaking, you need to worry about mold and wood rot.

We just had our roof replaced, because our last roof was replaced in 1977. In the San Jose area, we paid over $13,000 for the new roof which included replacing all the pipes and cover for the chimney, and wood rot repair.

They had to remove two layers of old roof.

They placed a plywood foundation before adding the new roof.

The contractor did an excellent job, and I have recommended them on Angie's List.

Depends on the leak. If it's few a few loose or missing shingles, you could probably do it. Otherwise, the leak could stem from a different location, rotting boards, or all the shingles are bad. Either way, lift a bundle and try and carry it up a ladder before you get to a head of yourself. Now multiple that bundle by the size of the job...