Ammendment/Addition to Royal Mail Module

I've been working with OC 1.5.1.3 and the Royal Mail shipping for a few days now and to say I'm having fun working with it is an understatement. One thing I have noticed, the current RM module, doesn't seem to take account of package weights. For example the current module gives the lowest price for std 1st class as over £1 (cant remeber exact figure at the moment), however if the item being sent were to fit the criteria below the price would be £0.46.
Letter - Max. 240mm (L) x 165mm (W) x 5mm (D) 100g or less 1st class - 46p 2nd class - 36p

To have a postage of over £1 the criteria would need to be:-
Letter - Max. 240mm (L) x 165mm (W) x 5mm (D) 100g or less 1st class recorded-£1.23
Large Letter - Max. 353mm (L) x 250mm (W) x 25mm (D) 250g or less 1st class £1.09

I wonder if it would be possible to make the following addition/ammendment (All dependant on the products having dimensions and weight defined)

1) That the program finds the maximum dimensions of the item(s) ordered which then gives the category ie Letter/Large Letter/Packet/Std Parcel
2) That the total weight of items is found. (plus any packaging) Which then gives the weight category
3) Delivery Method - selected by customer ie 1st, 2nd etc

Using http://www.royalmail.com/sites/default/ ... e_easy.pdf page 2 an array(?) could be made with the prices. Giving a result of Postage=array(size_category, total_weight, delivery_choice)

I have been working on some pseudo-code for this incomplete but if anyone is interested i'll post what I have. As I am not yet familiar with php I thought i'd throw it open to suggestions here. Thanks for reading this far and apologies for the long post