I think in today's times it is almost crazy to develop such a system from scratch.
There are hundreds of off-the-shelf systems which will do the job.
I don't know anything about the size of your organisation or the desire to tie this system in with other functions within the organisation (finance, invoicing, works order management). I personally work with Dynamics AX from Microsoft, but that's targetted rather at larger organisations.
You might want to start be reading this
article.
Regards,
Golf-Sierra