416133 Square Feet

I am moving my site to a Big Commerce store and I need to have my product calculated per sq ft. In other words when a customer clicks on one of my products, since it is flooring material instead of entering in a quanty 1,2,3, etc. they will need to enter the amount of sqft they need and the site will need to round up based on the quantiy in the material package. For example I sell rolls of underlayment they come in 100 sq ft rolls. If someone order 150 sq ft then obviously the site will need to round up to 200 sq ft, they will need two rolls. Also I have boxes of wood flooring that comes in different quantities so the site will work the same for each product and add the proper quantiy to cart. My site is currently with Yahoo, I am moving because I am tired of the Yahoo fees. But the site is still there and you can see how it works now. It will need to work the same with Big Commerce. [login to view URL] I will not work with any companies located outside of the USA. Thanks