I usually recommend people just take an existing PaaS and run with it. I'm wildly biased in this regard because I work on one as my day job.
Also because rolling your own is hard. Really really hard. We have literally hundreds of engineers in dozens of teams, and that doesn't count the engineers our partners have assigned. We've been cranking for years. It's just a lot of hard engineering for stuff you don't see until it arrives, and arrives unpleasantly.
Kubernetes makes it a lot easier, especially if you need lots of flexibility, but it still leaves you to assemble a lot of parts and management is left very much as an exercise for the reader.
If you build on Kubernetes, may I recommend Kubo to manage it? We built it with Google, but because it's based on BOSH you can deploy to AWS, GCP, Azure, OpenStack, vSphere and even bare metal with RackHD. BOSH by itself is a massive force multiplier for operations.