A few moons ago I was a home builder. I had a few skids, CTL's and a backhoe to backfill, cut driveways, rough grade for landscaping and general clean up. It worked well and was profitable as we saved enough money doing those things ourselves it allowed the use of the machine for other things like moving materials, cleaning streets, cleaning up trash, etc.
12 foundations a year IMO is not enough to invest in a big excavator to do your own excavation. All the normal costs of ownership, maintenance and labor add up and in the end you can hire it done for about the same money. Now if you're building 50-100 houses with basements the economics change. However, every business is different in how it's ran and what the ultimate goal of the business is.
When I was building my time was better spent managing subs than self performing. I could oversee many trades in the same amount of time I could self perform. As Georgia Iron said - I made more money being a manager.
The homebuilding industry in my area has transformed significantly since the crash of 2009. There are now two types of builders - national/regional big boys who spit out cookie cutters and the custom homebuilder. The small/medium local guy building affordable houses has went the way of the dodo unfortunately.
I've been solely in the commercial site work market since 2011, dabbled in it from 2005-2008 but nothing major. Commercial site work is not as profitable as building houses in the mid 2000's but I enjoy it more and since the market here has changed, I might as well as those times are gone.
Personally I don't want to build houses again. I loved the process of building and the creativity but the customers and builder chasing lawyers took all the fun out it..
I prefer the business to business work model of the commercial construction market. Profit is not a dirty word like it is dealing with retail customers. Not afraid to tell a PM or estimator that I don't need the experience - we are here to do a good job, on time, on budget and make a profit.
Just my $.02 others milage may vary.