The vast majority of installs in Mueller were retrofit, so I don't really know what's "normal" on new construction. That being said, you are buying a house from the builder and you should expect them to work with you.
Make it clear to the builder that it is fine if the installation doesn't take place until after the house is complete, but there are some things the builder will need to consider, that a solar installer can communicate in the planning/early building stages that will save you time in the future.
For example, a number of Mueller homes needed to have the electric box upgraded to make space for solar. This would a $25 cost if it was done at the beginning vs. several hundred dollars later. Also, it's possible that builder has a choice of where to put a roof vent - if so, there are going to be better vs. worse spots for the vents to go.
You'll get better information by calling a local solar installer and seeing what they recommend you do - it can't hurt to call. The vast majority of installs in Mueller have been completed by Lighthouse Solar, Texas Solar, Longhorn Solar and Circular Energy, but there are lots of good installers out there - here's the full Austin Energy list:
http://bit.ly/1u20cROGood luck!