Prior to scanning the suspect building, be sure you have your local prosecutors on board. Show them the technology; have them give their interpretation of the Kyllo decision. Demonstrate how the TI can help you gain additional evidence against the suspect without ever intruding into his personal space, or even stepping foot on his property.
Before you take the TI to the street on your first investigation, get formal training. One online article cannot even come close to giving you all the fundamentals necessary to legally and ethically perform a thermal scan of a structure. The Law Enforcement Thermographers' Association is the primary law enforcement trainer for TI use. Yes, I instruct for them. Yes, it's a plug. But, the reality is that if you plan to build indoor grow cases with a thermal imager, you need to be prepared for court. The LETA training is the only way I know to be certified and be ready.
Like every other thermal imaging application, the TI is not the silver bullet or ultimate tool. It is just one more tool in the toolbox that can help officers build a better case. Properly used, the TI can generate additional evidence to help secure the final search warrant, allowing you to go in and seize a lot of marijuana...and put a pot grower out of business.