Hi Simon!
Welcome to the forum! You may not be aware, but there is some info that the forum asks be completed prior to posting. I guarantee you've a better chance of getting a knowledgeable response if you do those steps.
viewtopic.php?f=1&t=4063
I'm just a fellow amateur, but I can tell you what I'd do with that space.... Basically just divide it into two (I'm not a big fan of the one studio I worked in that followed a live end dead end approach where it was all one room.) The specifics of what your goals are would matter a lot to how you would divide things up. How much isolation do you need? Do you want to maximize the control room? If so, I'd have a lengthwise control room. Do you want to maximize the recording area? If so, I'd consider a side facing control room. Each will have it's pitfalls since the space isn't big enough to make everything ideal. That slope to the celing may cause one to gravitate to the side facing control room style.
Have you looked at John's "small studio" sketchup plan which is available on this site? I'm using it myself for a similar shaped rectangular space. It seems like if you wanted to adapt that to your space, you'd have something as professional grade as it's reasonable to expect. Personally, I think John was pretty generous to post that plan.