The shepherds hut as we know it today took its shape in the 1800's when corrugated sheets (zinc) became available. It was the material for cladding the sides and the roof and very durable. Although the history of huts goes back much further.
They were mainly supplied by companies that sold farm implements, gates, hurdles, feed troughs, even farm sheds. A standard size would have been only about 9ft long unlike some of the monsters we see now. Weight was a consideration, if it was too big and therefore heavy, it would have been difficult to move about, as they were intended for.
As a hut was a considerable investment, only large farms and estates could justify the cost. A basic hut with no frills, just maybe one small window and a platform across the back wall for a bed would have been the cheapest option. Extras would have included a stove, fold down table, maybe another small window. There was of course no insulation. To have to sleep in one without a stove would have been a miserable experience especially in Winter.
Contrary to popular belief, a shepherd would use a hut for relatively short periods, more like weeks than months. At lambing time of course when he needed to be on hand at all times. Sickly or cold lambs were put in a pen under the bed (called a lamb rack)
If a flock of sheep was being fed on root crops like mangolds, the shepherd would need to be there to keep an eye on things, when they had eaten a field off, the flock, hut and the shepherd would move on to the next place. Huts were found predominantly in Southern England in open down land areas such as Dorset, Hampshire, Wiltshire etc.
At the end of the 2nd world war, farming was in a severely run down state following years of lack of investment and lack of labour. Food was still rationed into the early 50's Farming was in need of major investment to boost food production to feed the nation.
New methods of breeding and animal husbandry, new plant growing programmes were being tried. A wave of regeneration was in the air, out with the old, in with the new. There was no place for the humble shepherds hut in this brave new world and many were left abandoned in hedgerows, broken up or burned.