My family own a few properties and rent them out. We lose roughly a months rent when a tenant moves out, so they generally move out every two years. A boiler breaks, thats another months rent gone. Then you have to decorate in-between every tenant, thats another months rent. Wear and tear occurs a lot on things you wouldn't notice so you have to make a lot of random repairs. And if you think your going to get through a decade without having to spend at least £1,000 on a new kitchen and £1,000 on a new bathroom your mistaken. Also if the roof is your priority that could cost £9,000 when if it went wrong.
We had a tenant who refused to pay rent, he promised to pay us next month and failed. So we sent him a letter saying he had 2 months notice. However the day was one month out of it being a full 2 months notice. He had contacted the local council who decided to inform us this on the 7th week. So there we had lost 4 months rent and still had to give him 2 ADDITIONAL months notice. So we lost out on 6 months worth of rent. When we got the place back he had literally pissed all over the floors and filled the back yard with trash. This was a retaliation he was just a complete drugged up tramp.
On top of the 6 months no rent we had to completely renovate the place due to him letting his dogs shit everywhere and the floors were saturated in piss that the flooring was warped. And if your wondering why we didn't just take this guy to court it is because he had no job or nothing he would have made a low settlement of basically paying us back £10 a week for the rest of his life and we just preferred not to have anything to do with him.
I wouldn't recommend it unless you were buying a property that was situated in a student or low income area. I currently live in that type of area but your not going to get 10 years of good tenants.
So basically repairs and maintenance, refurbishment and having terrible tenants are all problems which you will encounter along the way. My family regret getting involved in it. The bad times can last almost a year and the money really isn't worth it.