Heidi forgot to add the most important bit.....Get someone else to do it!
The only advice I can give is to plan every detail out before you start the build i.e air-locks, internal features like some tree cut-offs etc....for instance it'll be much harder to install an air-lock after the framework is constructed.
As your not having a shed attached things should be a bit easier.....If you already have a flagged patio area outside your back door that you want incorporate then you'll have to fix your frame to that and the wall of your house with appropriate expanding fixing bolts.....and if you extend onto the garden to have a grassed area just lay a concrete foundation about 1 inch thick and lay a single course of bricks for the run to sit on (fix run to the bricks aswell).
Every vertical timber in ours is concreted into the ground to a depth of approx two foot and a course of bricks was set under the horizontals.....so it's very sturdy!
The frame should be simple enough to make.....just tell Gav's dad to make each side like a studded wall partition in a house( all equally spaced ofcourse)
Also when fixing the wire meshing make sure you pull it tight and keep the tension whilst hammering the u-nails in (use a screwdriver to lever it).....otherwise it'll look un-even and saggy which will spoil the look completely.
After I attached the wire on our run, I put some architrave over the visable sides of the frame on top of the joins in the wire meshing so it looked a much better finish
It's hard to describe what I mean so I'll post a few pics tomorrow to show it better!
One last thing I should mention is the roof.....It'll be much cheaper than you think to put a roof on, Ours was about ?35-40 with all the special fixings included.....and it'll finish the run off nicely!
p.s Don't forget to hire a slave for the day to be whipped if anything goes wrong and to make brews for the workers....good luck it'll be worth it!