I assume the garage did a pressure test and you have anti freeze in the engine. You have to pull the head or heads look for cracks between the cylinders. If no cracks send the head or heads to a machine shop for a pressure test. After this is done get an estimate to get a decent head or heads. They usually will give you a gasket set cheaper than a parts store. Your looking at a few hundred dollars at least. If your not helping I doubt he will do a complete head gasket for a couple cases of beer.