I've asked around about it, and it used to be widely practised from the 1600's to 1750's. If farm workers lost their jobs and were down on their luck, they'd ask permission from their ex-bosses if they could move onto common land and build a house (granted it was common land but the wealthy landowners/employers would have almost exclusive rights to the land) and they'd reply along the lines of "sure, if you can manage to build a house in 1 day you're more than welcome" so they'd quickly make one using all the stones (moraine) on moorland and make a basic house, strengthened up with peat and what-not.
They could then improve it throughout the year. Like anna said before, it explains all the isolated houses in "locationally disadvantaged areas" with in modern times, having quite small gardens, which I always wondered - a house in the middle of nowhere only having a 10 ft garden?
It also explains the nature of isolated farmhouses, a basic core - one story high, 10 ft across with rooms added as and when.
Unfortunately, the rule no longer applies, and has been wholly succeeded by modern day planning laws (in my area, all the common land is an SSSI, so new buildings are prohibited unless specifically authorised)
So, there we have it - every days a day at school eh?
My fortune awaits elsewhere