To get the Paradise City achievement in State of Decay 2 do the following:
Your settlement will have dotted orange outlines where different facilities can go. It'll also come with a few facilities already built, which will vary depending on where you settle your community. The achievement says you must build ten facilities, but upgrading previous facilities counts as well. Check your base building menu to see which items are needed for different facilities or their upgrades and when you've hit ten new or upgraded facilities, this one will unlock.