My main point is that, because housing takes a very long time to build en masse, you'd want the housing to start being built before people need it.
It's like any other strategic reserve we have. Since demand can spike, and we can rarely see the spikes coming, but we know they will come, just be prepared by subsidizing the development of that thing. We do it for food, oil, weapons, vaccines, you name it. If we know we will need it in the future anyway, and it take a long time to produce, we create strategic reserves. We should do that for housing.
Much easier to have a reserve of X, if X can be put in a warehouse and transported later.
After reading comments here, I think that US has plenty of cheap housing… but… cheap housing is in places where people don’t want to live. (Demand is low, price is low)
If you actually plan to use your own money to build a reserve of housing, better double-tripple check if anybodyz will want to live there.
"cost of an apartment needs to be at-or-below the cost to build that apartment"
That's not true, its that the cost to build the apartment is far too high and the cost is totally passed on to a the public, thereby hovering up any disposable income that might go towards having a child.
There can be a profit margin, but the cost needs to be low.