How can I create a SaaS solution (setting up each account)?

I have a web app that I'm currently selling online using ClientExec. I 开发者_C百科want to get away from ClientExec and use something like Chargify/Spreedly/etc. for the billing part, however my problem is how can I create each users account?

ClientExec currently creates a new cPanel account and subdomain for each user, which is nice, but overkill. My customers don't need access to that.

Can I setup subdomains using PHP?

How can I limit the users bandwidth and storage space?

Can this be done? Is there an app for this already?

If you are using cPanel you can use their SDK. If you are not using any control panel you will have to write some kind of script that will make changes to your httpd.conf and reload apache everytime you make any changes.