Custom Validations Before Booking

 I need to add Custom Validations in a Order which should be checked just before booking. To Implement this I added custom code in Custom.pll to Override the Functionality of Book Order button.

If validation fails I display a error message.

Qustion is, Can I somehow show the Errors like open messages?

For example if errors exists in Order, a new Screen appears which show the Errors per Line Number.

What I mean is that I want to implement my Custom, to work like the Standard Functionality does.

Thanks