Finish the module of calculation of area of a product to OpenCart

the Contractor refused, the piece was made, and some I dislike.
In General, the desired implementation of a module that would take the size of the product to the entered size, and then multiplied by the cost per m2 for different groups of goods.
Also, you do not want all goods to add each time a value of the width/height, I would like to make a band, and man chooses with regard to 1-5 mm step.

For different products need to be able to select the minimum/maximum size, maximum/minimum width/height. For each product a price per m2. Additionally, it may get a set of options that add/take away an amount or % of the amount.