International Shipping Rules setup

Hi there, Im just about to add international shipping to an existing website I built. I just wanted clarification with the approach im taking plus what formulas I would use in the ecart rules.

Since I am closely matching Royal Mail costs here in the UK and I am am going to be create weight tiers that match their costs. Also to make things simplier for the Admin I am also following Royal Mails approach to how they organise costs throughout the world, they have divided the world as follows:

UK
Europe
World Zone 1 (North America, South America, Middle East, Far East and South East Asia)
World Zone 2 (eg. Australia, New Zealand and Fiji)

So the above would be great since rather than having to enter in costs for each individual country the admin needs to only enter in the above (UK, Europe, Zone1 and Zone2).

Also Europe, Zone1 and Zone 2 will just require Standard shipping for now...

However UK will require...Collect from shop (so no shipping cost), Special Delivery and Recorded Delivery).

I have created 3 database tables
shippingoptions
shippinglocations
shippingcosts

The fields are as follows:

shippingoptions ->
ShippingOptionsID
ShippingOptionsType

shippinglocations ->
ShippingLocationID
ShippingLocationCountries
ShippingLocationZones

shippingcosts ->
ShippingCostsID
ShippingCostsType
ShippingCostsZone
ShippingCostsWeightFrom
ShippingCostsWeightTo
ShippingCostsValue

From the above table structure would this all seem logical? or am i potentially missing something?

I just need to work on the formulas to enter in the ecart shipping rules.

so for example

if the customer enters UK in the select box, another menu will appear which will allow them to select the records stored in the shippingoptions (eg, collect from store, special delivery or recorded delivery) then from the selected shippingoption together with the weight of all items in the cart the session variable to set. otherwise is another country is selected then there is no need to show the shipping options menu since standard delivery will be that countries default.

and to calcaulate the cost of shipping for example for UK the cost of special delivery will be for all items in the cart that are in the weight range of 0g to 1000g. And I be using the value stored in the table shippingcosts under the field ShippingCostsValue.

Also in addition I am adding a coupon system that the client wants to potentially use for giving their customers free delivery with a special coupon number (but the coupon system questions i will put into another thread).

So fromw aht I have written, with regard to the table structure, does this seem to be a logical approach or am i potentially going to run itno problems that i havent considered?

Chris