If you are interested in running a storage facility specifically for company records and documents, there are a number of things to consider.
First, keep in mind that, as with most businesses, startup costs have the potential to be very high. This is not like running a business out of your home, where you would need just your computer and a small supply of product. In this case, you are providing a service, and that service needs a location.
So, your first step will be to secure a place at which you will begin storing all the documents and records. Rental is one option, but might end up being cost prohibitive, so you should probably think about buying or building a facility. Then you have to think about what you will need in order to store everything. Shelving, to be sure, along with security systems, machinery (such as forklifts) to handle the heavy loads, boxes.
And let's not forget about staff. Because you'll be dealing with materials of a sensitive nature, you'll want to be sure you get trustworthy, loyal staff to work at your facility. This might mean paying them more than minimum wage, so your labor costs could add up quickly.
Of course, you will also need insurance. You will have a lot of very important documents on your hands, and you'll want to be sure you are protected in the case of a disaster like a fire, or in the unlikely event (assuming your security measures are strict) of theft. There are places out there that will offer insurance specifically for those in the records storage business, so you should do your research.
There are definite upsides to this business. For one thing, it won't really be all that complicated. All you're doing is storing some boxes, making sure a place stays clean and secure, and occasionally allowing clients access to their documents. You must maintain your retrieval system and records, but if you set it up correctly in the beginning, this shouldn't be an issue. If you offer clients the option of having their documents destroyed at your facility, that will add another layer to your level of work, but, again, the key will be setting up accurate and thorough practices and procedures from the beginning.
And there are plenty of businesses out there that will need your services. So you shouldn't have trouble finding clients, assuming you provide a high security environment for their records, and give them excellent support and customer service.