How difficult / realistic / expensive / probable is having my own house built? (Livermore: city hall, purchase)

[SyZ]

Assuming that I will not marry or have children, and I can do with a large master bedroom + a large office / study / entertainment / jigsaw puzzle room as well as a kitchen, bathroom (just one), garage with a washer and dryer unit inside, what are the logistics of making this happen?

Has anybody had their own home built on land they choose?

There is so much land in the Pleasanton / Dublin / Livermore area. There has to be a way (publicly) to see if land is already owned by the city for future development, or if there is a way to purchase it. I see all the huge homes on the western side of 680 going through Pleasanton, I'm assuming that is the work of somebody just going to city hall and saying 'hi, I have 50 million dollars. I want a home built on this land, make it happen and I'll move in in 10 years'

Standard 3 bedroom 2 bathroom single family residential homes in the area are 600k +. I refuse to believe if I built something on my own (if possible) it would amount to anywhere near that given the size of what I'm looking for

Thanks