Create an attribute with user provided info

I've looked through about 12-13 pages of the FAQ and not seen this particular issue. I need to create an attribute for square footage where my customer provides the amount of square footage of flooring they want to purchase. That specific value is then multiplied against a specific cost. I can't figure out how to do this. Originally, I created the attribute as a text attribute but I don't know how to get the user specified value to multiple against my unit cost to get a final price. Any suggestions? I am running on version 1.3.8a with no add-ons.

I'm surprised no one has replied so far. I'm assuming that I have to create a custom attribute but I haven't figured out how to do it yet. Any suggestions?

There's no such feature (multiplied pricing at the per-attribute level). But you can accomplish the same thing by setting the product price to be the sqft price, and then they just enter the number of sqft they want as the product-quantity.

ie: set product to $1.35
customer enters quantity of say 40

result: 40 x (1 sq ft @ $1.35/sq ft) = $54.00 when added to cart

prob wont work as im sure they probably want it to where the more you order the cheaper it becomes per sq ft.

if the amount of sq ft that you can order isnt that high i would recommend making a drop down box with number selections to modify the price