According to another post on here back in 2012, it was stated that according to EASA:
" (g) Flight time is recorded:
(1) for aeroplanes, touring motor gliders and powered-lift aircraft,
from the moment an aircraft first moves to taking off until the
moment it finally comes to rest at the end of the flight; "
When I did my hours building regardless of where is was, my attitude was "If I'm paying for it, I'm logging it"
I'm aware some do it differently, but if you're using the schools aircraft for personal use, not training with an instructor, you should be able to log it all. Personally I "usually" log flight time + 0.2 (6 minutes either side). Have done for years, no questions asked so far.
I'm not sure whether a school can tell you what to log if you're privately hiring?
There are many different opinions on this, and although I havn't really answerred your question, it's worth a thought.
P.S Tatenhill is a nice place for aircraft hire.