I looked around at what was out there and to be honest, it wasn't much help. Most people have taken a different approach, I wanted strength, durability, speed and convenience, built from the pallets I had to hand rather than searching out like sized ones, or buying them.
The location is a slight encroachment onto waste ground at the allotment, I didn't want it to appear too large but I did want to make certain it could store 2.5M bean canes, final dimensions are 1.8 x 2.7 exterior (1.8=wide enough, full size of "standard" feather edge and conveniently worked around a non-standard pallet I had), 2.7 is very conveniently 1.5 x 1.8, but that's more luck than judgement. Pent roof chosen to get most height, low wall facing access (again, so it appears smaller), 1.7 at the lower, 2.0 at the higher wall so most area is high enough to stand.
Did the best I could in short space of time with the groundworks, had to build up one edge, failed by about 2", but reckoned I could compensate in the build (which I did). Overall construction was jigsaw-piecing the pallets as I figured that would avoid fault lines, with some uber-strong-types forming the door edges. Cut and re-made pallets as required for the top layer of the walls. Breaking up pallets gave me my linking timbers and stuff, some slat removal/moving addition needed doing to support the cladding (top tip - a mattock is the best tool for non-destructive pallet disassembly, as you can lever with the width of the blade*). I gave up looking for ex-fence/shed feather edge and bought new (£100 total
). Made a door from two gravel boards and some more feather edge . Bought two bitumen sheets and two clear plastic for the roof (£30)
No, doesn't need planning over here, neither at home nor on the allotment (Below 2.5M, less than the size of Blenheim Palace, not near your neighbour, don't live in it, is the criteria). I was worried that some people on the allotments were going to get arsey, but I've only had positive feedback.
*ETA it is also the best tool for destructive disassembly if you have weak slats and/or all you need is the central 4x2 or whatever. Whack the slats front and back midway between the supports with the wide part of the mattock head to break them, this will release the central spars individually. You can then whack the slats with an ammer which should leave the nails in place on the cross member, there to be removed by claw, especially if they are annular ringed.