Design/Build is a method of project delivery in which one entity – the design/build team – works under a single contract with the project owner to provide design and construction services. One entity, one contract, one unified flow of work from initial concept through completion – thereby re-integrating the roles of designer and constructor. Design/build is also known as design/construct and single-source delivery. Across the country and around the world, design/build successfully delivers both horizontal and vertical construction projects with superior results – no matter what the project type!
Design/build is an alternative to design-bid-build. Under the latter approach, design and construction services are split by separate entities, separate contracts, separate work.
Design/build, design-bid-build and construction management are the three project delivery systems most commonly employed in North America today. Over the past 15 years, use of design/build has greatly accelerated in the United States, making this delivery method one of the most significant trends in design and construction today.
One Contract, One Integrated Team:
Design/build streamlines project delivery through a single contract between the owner and the design-build team. This simple but fundamental difference saves money and time by transforming the relationship between designers and builders in to an alliance which fosters collaboration and teamwork. United from the outset of every project, an integrated team readily incorporates BIM and LEED certification goals.
(source article - http://www.dbiamar.org/about/what-is-design-build/)