Joining businesses I understand what you mean.
I think it's a great idea to house different types of automotive businesses in the same complex, as you can refer work to one another and help each other grow. This is pretty common in the U.S., where many landlords build big garages with separate bays or multiple garages on a single property. But this isn't really a merger because all the businesses are still legally and financially independent.
Legal mergers typically happen in one of two ways...
1. One shop buys another shop to expand its operation or make inroads in another territory or market.
2. Two or more businesses combine their assets to create an entirely new company, in which each of the original business owners has a stake.
They both have pros and cons that depend on who you're working with and your ultimate goal.
If you're thinking about expanding internationally, talk to the guys at
Carlex Design. From what I can tell, they've developed a unique business model where they share their brandname and expertise with several outstanding shops across Europe.