To find a reliable roof waterproofing company, you can start by asking for recommendations from friends, family, or colleagues who have recently had waterproofing work done. You can also search online for companies in your area and read reviews from past clients to gauge their reputation and quality of work. It's essential to verify that the company is licensed, insured, and has experience with the type of waterproofing system needed for your roof. Finally, you can contact multiple companies to request quotes and compare their services and pricing before making a decision.