Not trying to be a drag....I'm into the AARP age, I remember toting schwag seedlings into the boonies by moonlight. just to grow some more schwag. We've been given a great opportunity to do this right - the grey area is mainly a problem for people who want to have a setup on the cheap. If it is a personal grow, start with a steel security cabinet or an old gun safe. Bolt it to the floor, cut your holes for cords and vents - LEO will be impressed if they ever show up and even if the neighbor's teenager kicks in your door while you are gone, they probably won't be able to carry your crop away or get to it.
Bigger grows - drystack brick, fill with cement and rebar, buy the best door you can stand buying. One cat I know has a 20 yard dumpster upside down in his barn, bolted to the floor. Take that! HAHAHA!