A while back I created a simple shell script for building and installing PHP 7 on Debian based systems. It checks out the PHP-7.0.0 branch of the PHP Git repo, runs configure to place everything under /usr/local/php7 and adds an init script for controlling the php7-fpm process that provides a CGI socket at 127.0.0.1:9007.
There are also pre-built packages of PHP 7 provided by Zend.