Where I live, it’s getting really cold, and I am looking for good places to ride indoors. does anyone have suggestions as to where to ride that might be free?
what kind of riding do you do, I use my garage
You might want to start with a planet, to give us somewhat of an idea where you are? 
Mostly you’re going to find that without doing paperwork, getting insurance, etc. it can be really hard to get anyone to formally let you ride in their building. It’s liability.
Others may chime in with stuff that has worked for them. Your best bet, in my experience, is to join a unicycle club, if available. If not, create a unicycle club. Then make sure at least one of your members goes to a church that has a gym, or similar. Then see if they’ll let you ride in there. This can take a lot of effort, but be very, very worth it.
My company is moving to a new building, and in that building we’re going to have a large open space, with a vinyl tile floor and 9’ ceiling. I think they’re going to let me ride in there, at least sometimes, and possibly even teach lessons or have a unicycle club in there! This is extremely rare, and hasn’t actually happened yet, but we’ll see…