apt-transport-https
First, if you are on Ubuntu Cosmic, you need to manually compile json-c because the version provided is 0.12.1, but sway requires at least version 0.13. It is pretty straight forward, so take a look here.
Then, we need to install common dependencies between wlroots and sway-1.0.
sudo apt install gcc pkgconf meson ninja-build libwayland-dev libinput-dev libcap-dev
Secondly, we need to install wlroots dependencies.