There are five books to my knowledge written by Roy Clarke relating to Summer Wine.
The original novel which was the basis for "Getting Sam Home" - two editions, one with Foggy replacing Blamire.
Gala Week - novel in Summer Wine Chronicles which involve Seymour
The Moonbather - novel in Summer Wine Chronicles which involve Seymour
Summer Wine Country - with text supporting (as if written by Clegg) some wonderful photographs, a hardback
The scripts of the pilot and the first series.
I think he may also have been involved with the Keeping Up Appearances book. Yes he is credited alongside Jonathan Rice.
I have long looked for books by Roy and have never discovered any others: there are other Roy Clarkes writing as well to confuse the issue!
Most are available on Amazon used at £0.01 plus postage apart from the scripts which is currently £11.99 - probably the rarest one.