Object-oriented Modeling problem - Metal Ordering

A company sells stock metal and we need an on-line ordering system. The stock comprises bars of various metals in various cross-sectional forms. The cost of a length of material depends on the weight and the material. Currently bars are sold in th e following metals:>
MetalSpecific weight in Kg/cubic mprice per Kilo in £
aluminum256390
brass839445
copper720960
stainless steel7353120

The metal bars have the following cross-sections, and the formula for computing their cross-sectional area are given
Shapearea formula
square bara*a where a is the width of the bar
rectangular bara*bwhere a is the width, b the height
round barPi*(d*d)/4where d is the diameter, Pi is 3.14159
hexagonal bar2.598*a*awhere a is the length of an edge
cylinderPi*b*(D-b)/4where D is the outer diameter, b the wall width

A product is a length of a metal in a specific form - eg. 6m long bars 10mm square. A web interface is required to allow a user to place an order, comprising several items. As a first step in developing this system, develop a 3 tier system using a web browser and Oracle 9i to allow the user to choose a product and a number of units. The system will then cost the item, reporting the total weight and cost.

Work for me to do