Offering to Buy a Neighbors Home

I bought a duplex in 2019. The next door neighbors are very quiet and keep to themselves. I've had less than 5 very brief interactions with them over the years (They are on a corner and their door/driveway is on the adjacent street). Their roof is in pretty rough shape and is starting to "shed" into my lawn. They have owned the duplex for 15+ years and currently occupy both units. I've been thinking about approaching them about their roof but I've recently had thoughts about trying to work out a deal to buy their home. I'm wondering if anyone who has had any experience dealing with a similar situation would mind sharing any advice on how to address the initial conversation. Thanks!