Writing a module for very custom products

Hello,

I am currently searching for an easy way to define products where the customer is able to enter his own specifications for. For Example if the customer wants to buy a cupboard he should be able to enter the height and width of the cupboard.

My idea was to write an extension, which allows the user, to enter the data in the specifications / attributes, before (!) he adds it to basket.

Any other suggestions of where to begin developing such an extension?

Thanks in advance

Stefan

as far as I know there are existing product configurators available - I just do not remember exactly who was the developer, please use the forums search engine