People don’t go down the build a house route because it’s so much harder than walking into a finished house, plus at least in my area there really aren’t many plots of land around, they have all been taken already. Also to my knowledge you can’t get a mortgage on essentially nothing to use to pay for the land and builders so you need £100K or what ever it costs floating around.
Then there’s the hassle of dealing with, local authorities, builders, suppliers, plumbers, electricians, carpet fitters, kitchen fitters etc you get the idea. Plus being able to project manage something like this whilst working full time makes it even harder.
It’s a brilliant investment and a great idea in theory but it takes a lot to go ahead with something this big without knowing if your even going to like the house at the end of it.