I am currently using ModernBill, although it's great, I can't help but think a custom billing system for my business would be much better. I am considering this option, but I'm wondering if anyone here has a custom billing system, and any suggestions for someone bulding one..

I went the custom billing system route because I hated QuickBooks. I'm very happy with my decision but it would have cost a lot less to stick with a third party system.

The reason I prefer the custom solution is that I am in complete control over all aspects of the system. I can taylor it to my specific needs. I'm not stuck with QuickBooks' crappy reports. I don't have to pay Intuit more money to send out e-mails with .pdf's attached. If I think of a new way of doing something or a new way to look at something or a client suggests a new feature, I can go in and add it. It's very flexible.

It's hard to provide any specific tips because I don't know what you want your system to do. I guess the best advice I can give you is to figure out what you don't like about the available options (QuickBooks, ModernBill), and design your system so that it fixes these problems. After spending a bunch of time (time=money) building my custom billing system, I'm convinced that it was the right decision for me and my business.