home office can usually be justified as for the enjoyment of the dwelling house or whatever it is - as long as you don't have employees coming in everyday!
Subbed!
My uncle and I are about to build a ~22ft by ~10ft living area / log-cabin in the garden - should be done within the next 10 days. Going over to finalize with him tomorrow evening.
He's a builder (has been for a long time), has done a log-cabin for his own place too and has roughly come up with a cost of materials at £1500.
For inspiration, I bookmarked this guy's self-build a while back;
http://www.vwt4forum.co.uk/showpost.php?p=1163154&postcount=8
It'll be a couple of years before I attempt one, though.