In Caversham, just outside the town centre are 3 pubs that do a good Sunday roast: The Griffin, Prince of Wales and Clifton Arms, they all have parking. A bit further out on the way to Mapledurham is the Pack Saddle. Hope this helps
The Griffin is very good but does get busy. The Pack Saddle is a bit more out in the country if that is what you are looking for and has a very good reputation too. Must go and mop the kitchen floor now!