The contractor, which recently opened an office in Manchester, has been appointed by Inchcape Estates.
Robertson will demolish the existing offices and part of the warehouse unit. The building will then be extended, re-clad and fitted out to form a new showroom and workshop.
The car park to the rear of the building will be extended and a new road will also form a new access point from Sealand Road. This will also allow room for more than 100 used cars to be displayed.
Robertson regional managing director Andy McLeod, said: “Our track record in delivering leading edge projects has resulted in this contract win. We have successfully completed a number of projects for Inchcape in the northeast of England and are looking forward to successfully delivering a project for them in the northwest.”
Work is due to be complete in early summer 2013.
Robertson’s new Manchester office is also working on a £9.4m community hospital in Cockermouth and a £4.2m health centre at Cleator Moor.