Good afternoon Tim
That looks good. Are you sheeting it to keep the rain off ?
Here's my two penn'orth. I built the sides of my last workshop on my own in sections made the same width as the OSB lining. Every four foot (or was it 1200 mm - it is important), I bolted adjacent panels together.
If you can, cut both the outside studs of each frame together in one cut, and do the same for the top and bottom. Even if the panel isn't square, it should then be a parallelogram and therefore easier to square up if needed. I screwed wood to the floor to make a jig to assemble the frames.
If the diagonals aren't equal, make a loop of rope and drop it over the corners of the long diagonal. You can then tighten it by putting a batten through the loop about midway between the corners and twisting the rope to shorten the long diagonal, pulling the frame square. Then fit the intermediate studs and brace the panel with a bit of roofing lath.
Erect a frame in a corner and brace it temporarily. I put an additional stud on the outside of the one corner frame. This effectively means a 4" square upright on the side one frame which fits onto the 4" face of the 4 x 2 end stud of the other corner frame. Stick the adjacent frame up round the corner and clamp the two frames together. Fix the bases of the frames to the floor nice and square. If your floor is horizontal all the studs should be vertical. If they are, bolt the frames together in the corner and square the top edges.
( A 3-4-5 triangle of roofing lath comes in handy). Temporarily brace the ends furthest from the corner.
Dont forget to recess the bolt heads on the outside corners so that your cladding will sit flush. Make the counterbores big enough to get a socket head on the bolt on top of a decent sized washer. Brace the top edges of the frames across the diagonal and move on to the next corner. Fill in the gap between the corners, perhaps including a non standard frame and carry on round the base till the panels meet. Check the internal diagonals at the bottom of the corner suds. Then fix your metalwork over the sole plates. Check the diagonals at the top of the corner studs, fit some temporary bracing, fit the wall plate and you are ready for the roof.
I effectively ended up with a 6 x 4 stud on each corner and a 4 x 4 at the junctions of the panels. If I was doing this for a living, I'd probably look for a cheaper solution but I wanted a bit more strength to support the roof anyway.
The one problem you may find is that the width of the windows has to be small enough to fit within a four foot panel.
Some general observations ...
I nailed all my frames together, but If I do another one, I'll use screws. It's easier on the arm and 'undoable' if things go pear shaped. If you do use screws, go for Torx heads and think about investing in an impact driver.
A couple of clamps like these ...
http://www.toolstation.com/shop/p19836?searchstr=clamps
are worth their weight in gold.
If you're having a single pitched roof this won't apply. Dont set your windows too high. If you do, any (vertically hinged ) opening lights will foul any overhanging rafters. DAMHIKT. It's now a security feature.
When you fit the cladding, as a possible alternative to Mike's detail, think about ripping the corner out of a 2 x 2 to give an L shaped section. Fit that to the corner studs and board up to it to keep the corners neat.
Good luck with the next bit.
Cheers
Dave