We are about to start on our first 14' hut, which is the limit to which we will go (we certainly don't build them wider, as the proportions would be all wrong on a shepherd's hut) but a bit longer will work OK.  It allows our customer to add a shower in the corner, plus a woodburner and small kitchen area. 

We are often asked about the base on which the hut should stand.  We have arrived on site a few times to find some pretty bad attempts at a level base, sometimes even that were made by a local 'professional' in such things.  It's a shame when we roll a hut onto a new concrete slab base and the slabs crack in half.  At the very least the hut needs to stand on fairly level ground.  It it's soft ground, or will get soft in winter, there needs to be something to spread the load under each wheel, such as treated timber planks, railway sleepers, flagstones etc.  Huts look good standing on grass, but if you want a more formal area around the hut then a border of railway sleepers, dug in level, with a base of landscape fabric filled with scalpings or gravel looks good.  We have sited huts on properly prepared flagstone bases, and in the right setting this looks very smart, as does a brick base.  

Getting the base level may not that easy, especially on sloping ground.  What doesnt work (and we've seen it more than once!) is to dig two holes on the high side of the slope to drop the wheels into.  It's a bit like burying half the wheels of the hut, which just isn't right.