I actually really resent the McMansion obsession in housing design for the last 40 years. Houses are not built to be functional or comfortable. They're built to be a status symbol. A shoddily built, poorly insulated, overpriced status symbol.
I would already own a house if there were reasonably sized houses on the market that were well built. But there aren't. There are acres of McMansions springing up everywhere, but no sensible, functional houses.
You can actually build the house you want. There are empty lots on the market most places. That's what we did. Our house is so well insulated and passive-solar heated that here in Iowa, even with the -20+ temperatures we've just had, the furnace doesn't run all day.
The financing required to buy the land and build a new house is more difficult than buying an existing house.
Building a new house typically requires more collateral because the bank is wary of loaning the money and then the project falling apart before its finished. When that happens, all they can reposes is parts of a house that aren't even worth (on the open market) the cost of the building materials and work already put into it.
It's not a huge deal if you go with an existing builder with lots of experience, especially if they already have a relationship with the bank... but if you want to save money by being your own general contractor or do any work yourself, that's when you encounter the most problems.
McMansions are actually quite functional and comfortable for the way upper-middle class Americans live today (at least those who can afford the utility bills and to pay others for cleaning and maintenance). The major real estate developers hire sociologists to study the lifestyles of real families and then incorporate the results into architecture. For example by putting a large window with a clear view of the entire back yard above the kitchen sink so that a parent can simultaneously cook dinner and supervise small children playing outside.
I would already own a house if there were reasonably sized houses on the market that were well built. But there aren't. There are acres of McMansions springing up everywhere, but no sensible, functional houses.