We need to modify our shop selling window blinds so customers were able to put custom width and height (both in millimeters) and the price were calculated based on that. These two values (width and height) should be also visible in the shopping cart and on the invoice next to product name (i.e. roller blind 2345 x 1984). The price need to be calculated according to the formula: width/1000 * height/1000 *price_per_sq_meter, and the price price_per_sq_meter sould be settable somwhere at the back office for a particular product (different products may have different prices per sq meter). It also should be possible to have in the shop regular products (with no size inputs).