I tend to forget to read the height the plant gets at maturity. I bought a Crepe Myrtle (bush) several years ago. I planted it along side my other shrubs close to my front door. Today in order to see the beautiful blooms one has to look up to the roof of my house to see them. In fact most of the blooming area is atleast 6 to 10 feet past my gutters.
Check out this article:
http://www.clemson.edu/extension/hgic/plants/landscape/trees/hgic1009.html
In particular:
When a large crape myrtle is in a spot where a low, compact plant is desired, there are two options: (1) dig up the offending specimen and then plant a dwarf or smaller cultivar that requires little to no maintenance, or (2) prune the stems back to about six inches above the ground each year. Severe pruning will not kill or injure a healthy crape myrtle.