The issue of renting to someone is the potential impact his work may have on your business. The customer will not separate his work from yours, they will just identify the building and your name. If he does a job that doesn't meet your quality standards, you will pay the price. I would either hire him to do transmission builds for your customers, bring him on as a partner, or help him find a small location somewhere. These situations always look good in theory, but they always seem to end up in a bad way. If he is doing work for his customers, you have no say in the quality of his work, when he works, or how he works...he is renting the space. Safety, housekeeping, tools, money, customers, and time are all factors that matter a great deal. Basically its like getting married to someone who squeezes the toothpaste, when you prefer to flatten it from the bottom. If you do decide to let him rent, I would have all this lined out in a contract or agreement.