Don't get common plecos. I bought one for my 20 gallon tank. He grew to be around 10 inches long and he made his territory under a rock formation I had built for him. That was good, he used his tail to sweep all of my sand substrate out of his cave. Made a mess but ok, then I caught him sucking on the side of my gold fish. I thought it had hole in the head disease but it was him eating the poor thing.
So I moved the pleco into a 125 gallon tank. Again he had a cave for his territory and he swept it clean. He grew to be maybe 18". He was huge. He started going after my angel fish.
So I moved him into a solitary tank on my back porch for the summer. He just kept getting bigger and bigger. Eventually I talked my LFS into taking him. I had no where left to put him and I don't have room for another solitary 125 gallon tank.
He was a nice fish and very interesting to watch but he just grew way too big. I had no idea they grew that big when I bought him. I wouldn't have bought him if I knew.
Just note, plecos can be very territorial and while you think of them as algae eaters they do eat fish as well.