Add a feature to vtiger for booking an asset by a user or by a client over customer portal

I need someone to add a feature to vtiger so that users of vtiger and clients (over the customer portal) would be able to book an asset like a car or conference room over a certain period of time (for a few hours or for a day for example). It would be necessary that users of vtiger or clients (over the customer portal) see that a certain asset is reserved for a period of time (in a calender grid of that asset) and that no one else can use it during that time. Later, the client would be charged for using that asset.