I think you have to separate the idea of the network and the services running on it.
The network itself will be a simple business grade network with appropriate ethernet/wireless access points etc, and perhaps some VPN tunnels to connect his different sites. That you should have no problem installing.
But the functionality of a cyber cafe style billing system? or even hotel booking system etc is specialist software. What you really want to do unless you are very advanced and confident in doing it all yourself, is look for a specialist software company that will do this hotel stuff for the client and offer your services to assist in setting things up as the IT litterate "man on the ground". You can still install all the hardware and the network kit, and still bill for your time working with the other company t set up the software if required.
Perhaps they are already using software like this and it just needs a little know how to get it working as they would like?