Run these commands :
wget -O - http://repo.ada-consult.com/repo.ada-consult.com.gpg.key | sudo apt-key add -
sudo sh -c "echo 'deb http://repo.ada-consult.com/ natty main' > /etc/apt/sources.list.d/ada-consult.list"
sudo apt-get update
To add a package, follow these instructions :
Sign the debian package
dpkg-sig --sign builder mypackage_0.1.2_amd64.deb
Add it to the repository
cd /path/to/repository
reprepro -Vb . includedeb natty /path/to/package/mypackage_0.1.2_amd64.deb
http://blog.mycrot.ch/2011/04/26/creating-your-own-signed-apt-repository-and-debian-packages/