Here are some advantages of the Design-Build process.

Assigns design and construction to a single party, allowing some construction work to begin before the final design is completed.
gives singular responsibility- single point of contact for quality, cost, and schedule.
reduces administration and inspection costs.
reduces or eliminates change orders and claims due to "errors and omissions."
allows maximum contractor flexibility in the selection of innovative designs, materials, and construction techniques.
provides expertise not available in-house (Example- Intelligent Transportation Systems).
Warranty provides a warranty provision that promotes quality/performance during warranty period.