I own and operate a self-storage property. It is an excellent business. There is a reason that storage properties are among the lowest for bankruptcies. They are not passive income - you do need to be involved and active - but they are diverse income. If one or five tenants don't pay rent you have many others to cover your costs. That is very different from a house or apartment rental.
In the easiest months we are completely full, nobody moves in or out, and I spend about an hour tallying the reciepts and paying the bills. In the harder months there is some maintenance issue and some turnover.
You do need to have some time available to operate the property, or be willing to pay someone else. I think industry standard is between 6-9% of rents to have it managed by someone else, but I haven't looked all that much into it because I live nearby and operate it myself.
Things to look for:
1. Low maintenance. Look for simple construction - ideally cinderblock walls, metal roof, metal doors.
2. Good security system. Ideally something that can be operated remotely so you don't need to keep staff on site.
3. Location. In or near a population centre, ideally near a busy road.
You have to be ruthless with people who don't pay. Be very clear when they rent what will happen to their stuff if they stop paying. Get rid of it after no more than a month. Automate it if possible.
