Andy, this is awesome... I'm exceedingly jealous of your space!
I'll soon be embarking on a shed build of my own which will be limited to 4.5m x 1.4m... I'll lose about 1m of length to store the mower/whipper snipper/etc. but the rest will be project storage doubling as a spray and blasting booth.
I'm going to try to be fancy and make the side able to fold out so I gain an extra 1m of width to get some room when spraying.
My one crucial question for you... how sound proof have you been able to make the compressor compartment without inhibiting air flow? I'm intending to insulate all walls and the roof for noise and I'm hoping I can get the compressor noise down by having it in as sound proof an enclosure I can make and sitting it on some foam rubber or something as well. Most of my working time on projects is at night, and unfortunately the shed will be on the side of the house near the bedroom and I'm not sure if I'll be able to make it quiet enough to use at night without disturbing my wife or neighbours...
Ok, so insulating the whole of your shop is also good, in reguards to the compressor, my enclosure is 3 sided and goes from floor roof, it also has exposed insulation retained by mesh on all the walls. It's important to remember your not trying to confine the noise (making a small enclosure) but reduse it
this is why my enclosure its floor to roof and so does the insulation. I have a large hole in the access door to allow plenty of airflow and with these measures it's no much louder that an old fridge compressorv
pretty good me thinks. cheers Andy