Phil
Sorry, it's still a little complicated for a depot IMHO, the amount of points you have there would suit a much larger depot, rather than a fuel servicing point, I understand what's trying to be accomplished but less is more.
The red loop doesn't appear to serve a purpose, from a real railway perspective. If each square is 12" long then you can only store two locos and as a run round, run round for what? You can achieve exactly the same path via the other track and points, railways never, ok, rarely, replicate trackwork or pathing.
Within that space I think a two road single ended shed would be better at the front right hand end, something like Shirebrook with a fuel rack out front, along the back would be a line, single, or if you boards are wider double, your locos can enter and exit via that and it allows you to run a simple passenger service, two car DMU etc, your fiddle yards are only two tracks wide. Your dead or stored locos would be at front left, but I'd question how many need storing, if they can't be fixed locally and they can be towed then they would normally be towed off pretty quick to a depot that could fix them, two or three stored would be your max I think.
Serviced locos ready for the next service are a different matter, at Peterborough those were normally shunted down to the two roads by the station I believe.
Your double cross over is actually working against you operationally, its making it too easy to get from the shed, middle right I presume to the front track or storage, if you loose one of those cross overs it will entail a double shunt to store locos or to release and thus add more operational interest and thinking about how to get locos in and out. Try and see what it looks like with the right hand cross over removed and the left hand one put there in its place, you'd have more head shunt space to store locos with.
Without buildings and standing back a bit from the screen the current layout looks more like the approach to Waterloo than a small service depot and once you add buildings then it will get very cramped and you may not actually have room to add the shed, even single track sheds are quite a bit wider than we probably imagine. That may well be the effect your looking for, I dunno.
Hope this isn't taken the wrong way, no offence intended, just ideas in the pot, I'm heading back to the bunker LOL.