I thought a lot about this in the past and wouldn't do this if I were you. Houses are typically not set up well for this type of storage with stairs and rooms and what not. If you're at the point where you need that much additional storage, you'd be better off renting self-storage space for the short-term while looking for/working towards a longer term solution. Finding a pre-existing warehouse close to your house for a decent price is pretty difficult in most areas, but not impossible. Have you talked with commercial landlords and looked at Craigslist? I constantly look at the commercial stuff available around me and it's all wildly expensive, but have found some very affordable places off the beaten path. The idea of renting retail space for storage is not a smart one IMHO. Retail space is typically more expensive and comes with all sorts of lease covenants that pretty much require you to be, you know, a retail store. Sure, you might be able to find some desperate landlord willing to forego some of that, but then you're probably renting storage space with some amount of breakable glass on its front right next door to the internet gambling parlor, a car audio store with a "z" in its name instead of an "s," and a vape shop. The option that is a bigger pain, but makes sense if you're in this for the long haul is to find commercial land and develop it with storage that suits your needs. Trust me if you're starting to operate on a larger scale, you are going to want/need the ability to move things around on pallets using a forklift/pallet jack before long. Unless you have some very weird houses in your area, you aren't going to find that in a house. Your back will thank you.