Single ply roof guarantees usually cover 15-20 years, but many roofs last 25-40...

https://trevorsinspiringnews.yousher.com/how-long-should-a-quality-membrane-roof-last-on-a-distribution-centre

Single ply roof guarantees usually cover 15-20 years, but many roofs last 25-40 years in practice. The difference comes down to things like weather, wear and tear, and maintenance