Product options

Assign options to products eg:

T-shirt product
Options: size[s,m,l]colour[red,green,blue]

Each option can modify the dimensions,weight and price.

id, name, price, size etc

With a habtm type join to products such as

id, product_id, option_id, price, size etc

You can specify the cost, price etc in the option and all products with that option will have the default or overload it for specific products in the join

Products using options would not use the stock on the product, but rather the stock on the option.

Would need to figure out stock for mixed options some how, eg small red shirt vs large red shirt.