To be able to use the packages built by the server you can add it directly to your pacman.conf.
To add the custom repository to your pacman configuration you can simply append the following section to your /etc/pacman.conf file.
[aurbuild]
Server = http://your-server-domain-or-ip/repo
Make sure to replace aurbuild with the name you put in the server configuration under repo_name in the server config.
If you do not enable signing you will need to add the following line to disable signature checking.
SigLevel = Optional TrustAll