On a slightly different subject there was yet another survey in the paper yesterday which reckoned Australia and in particular Sydney and Melbourne were amongst the most expensive cities in the world, how do they compare with the rest of the country as I am hoping to retire to Aus.
House prices in Sydney are very high unless you are willing to live a long way out. Not so sure about Melbourne. Where we live, in the rainforest in the hills west of Cairns, which is a tourist area, houses are literally half the cost, e.g. reasonable 3 bedroom around $400,000, sometimes a bit less. If you are coming here, also have a good look at the climate in your preferred areas.
So you should be alright.
I'm guessing the OP needs to check the zoning on each piece of land he finds. If he gets some land up in the mountains some where, I'll bet the likelihood of building it himself (or partially himself) will be higher than if he wants to built it in the center of Zurich.
Here is my story which may help you. My dad bought an old house in a commune in Vaud about 30 years ago. He completely redid it, including making a cellar, making additional parts to the house which pretty much doubled its size, made a separated studio apartment and 4 garages. It took him a good 2-3 years to finish it up, working on it daily after work and week-ends. He made the plans himself and hired a few workers by the hour to help from time to time in the week-ends. He handled all the negotiations with suppliers, equipment/machinery renters, permits, etc..by himself. He knew only basic french (really basic) and with a banker background in his early career (very limited funds). The only thing he did himself that was supposed to be done by an expert was connecting to the electrical grid, but no one ever said a thing.
So if you have the patience, I think it is doable. Now remember that was 30 years ago, things might have changed.
Good luck!