A.L.
We bought a "built to order" home 9 years ago from Milburn (now Horton). Things we wished we'd done:
We went after my husband went off work one day, to the showroom where details were chosen. We were the last appointment of the day, and I guess the lady wanted to go home. She didn't try to talk us into nearly as many upgrades as we had expected her to. But there are some that, in hindsight, we wish we'd sprung for:
Paid extra to have a sprinkler system installed. True, it adds a little to your monthly payment, but that is a lot less painful than several thousand dollars all at once, further down the line. Especially since new developments tend to have homeowners associations, with rules regulating taking care of at least your front lawn, so you either have to buy a sprinkler system, or do what we're doing, and spend every Wednesday and Saturday evening carefully moving sprinklers around, so you get full coverage on the yard without running water down the street.
Getting an outside light installed on BOTH sides of the garage, instead of just one.
In the kitchen, get the deeper sink AND the tall faucet. We got just the deeper sink - wish we'd done both.
Get the bigger hot water heater, or a hybrid, if you can. The smaller one SEEMS like the better/cheaper option, until you have to take a cold shower, because someone forgot and ran the dishwasher after the kids took their baths.
You will have the option of where you want to put electrical outlets, light switches, cable outlets, and phone jacks. The electrical outlets and switches might seem intuitive, and we did okay, but we wish we'd had cable outlets put in every room. We aren't television-in-the-bedroom people, but we've moved our office three times, and the computer is hooked up through the cable. It's a pain to call and have a new cable outlet installed.
Our builder used cheap paint. We've had to primer AND paint every room - and the paint we had soaks it up like chalk, so we don't trust the paint/primer combo. So if they offer a higher grade of paint, you might look into that - it will save you time and money later, even if you don't decide to change colors.
Also, if you choose carpet, the builder will insist that you choose a neutral color, or pay a premium. This is because you still have the chance to back out, and they have a better chance of selling houses with neutral colors. Be aware of this, if you have your heart set on red or dark blue carpet.
Don't be afraid to ask what you can get. I remember our builder was offering a "combo" package that we didn't want, and were able to get the master bath upgrade instead. It never hurts to see what you can mix and match!