Build an updatable agent for inventory tool

I've been looking for some pointers in how to build an agent that can be updated that would be used for an inventory tool. The fact is that we would like to create a custom tool to inventory our hardware. The agent would be installed at every new device. His task would be to inventory the device and update or insert those records into a SQL database.

Can anyone point me at least in the right direction?

thnx!