I'm watching the second episode on BBC2 right now, it's exactly the same as the first.
The "self-builder", widowed Sumati (which the voice over pronounces "Timothy", go figure) pays £100k for the land/plot* and spends the rest of her life savings - £50,000 - on building the actual cottage she will live in as cheaply as possible, using salvaged materials etc.
These Homey fuckers, honestly. Why don't they cut the crap and do a series called "The plot of land which cost £100k"? That's the so-called self-builder's biggest problem, designing and building a house and having it built for somewhere between £50k and £100k is the rewarding and easy bit.
* The way the story tells it, she bought what she thought was a habitable little cottage for £100k and had some money left over to do it up and is disappointed to learn it is a wreck. But it is clear from the context that any sane person would have know that the old building was uninhabitable, which is why she could acquire it so cheaply, and the old cottage is demolished in the first few minutes of the programme and she starts again from scratch.