Install reprepro:
apt-get install reprepro
Create dirs:
mkdir -p /var/www/reprepro/ubuntu/{conf,dists,incoming,indices,logs,pool,project,tmp}
cd /var/www/reprepro/ubuntu/
Create distributions file:
cat >> /var/www/reprepro/ubuntu/conf/distributions << EOF
Origin: Your Name
Label: Your repository name
Codename: karmic
Architectures: i386 amd64 source
Components: main
Description: Description of repository you are creating
SignWith: YOUR-KEY-ID
EOF
Create options:
cat >> /var/www/reprepro/ubuntu/conf/options << EOF
ask-passphrase
basedir .
EOF
Finally add some debs!
reprepro includedeb xenial /path/to/package_1.0-1.deb