Hey guys, how are you?

Guys, I'm from Brazil and I started with Drupal 5 or 6 months ago, and now I'm with a great doubt to customize drupal.
The project is an e-commerce and I'm using ubercart.

The client is asking for a required page before access the cart list!

For example:

The normal way is = Access the Product Page -> Add to Cart -> Cart List -> Checkout -> Finalize the purchase.

What I need to do = Access the Product Page -> Add to Cart -> Required Page -> Cart List -> Checkout - Finalize the purchase.

This page is to customize the product, with a customized module that I created. I already did something, but I fell that is wrong.
What I did was: I created the page in admin panel, and in the theme folder I created a file to customize that page.

Is there some way prettier to make this issue?

Thanks a lot.