The firm was pitched against rivals Bam, Galliford Try and Kier for the service station job, which is due to get underway in a few weeks.
The scheme between M5 Junctions 11a and 12 at Brookthorpe is the brainchild of Gloucestershire Gateway Trust and Westmoreland.
Architect Glen Howells has designed a timber-framed building that will appear to be buried into the landscape to reduce its environmental impact.