Donnie,
Rates certainly have an impact on whether consumers purchase a home and what price home they can afford and this rightly should be a concern. But we are not disussing what rates are, but what they might be in the future -- an unknown. The risk that rates could increase is always a factor when building. Since you have built before you have taken that risk in the past. After the house was built you may have closed on a rate that was less than you expected or it might have been more unless you purchased a commitment. And that is my point. You must decide on the risk that you are willing to take to get what you want. My personal opinion, which is worth what you are paying for it
, is that the risk is fairly low that rates will be dramatically higher in the next six to eight months. But if I am wrong I'm not the one that will be making that payment, you will. When you plan with imperfect infomation (and all plans are made with imperfect information) you must live with the decision. There are things you can do to mitigate risk -- buy a commitment, don't build buy existing, put a financing contigency in your contract with the builder limiting whether you have to close if rates go above a certain amount, etc. -- but you can't eliminate it.
So you aren't missing anything. It sounds like you are considering your options and being thoughtful with you plans. My point wasn't to say that interest rates don't influence purchasing decisions, just that you shouldn't buy a house you don't like due to a possible change, up or down, in interest rates. That's the tail wagging the dog. You don't buy a house to get a loan, you get a loan to buy a house.
Good luck! I'm confident that on reflection you will make the choice that is right for you and your family.