Product price based on custom fields

[max.bertolini]

Hi all,

I'm new in VirtueMart so my question could be stupid...
I wish to create for a product a list of custom fields that specify the product characteristics, each of these custom fileds should have a dropdown with a list of possible values.

i.e.
Material:
    --- plastic
    --- metal

The price of the product should change based on the selection made by the shopper...

I have no idea on how to do it...

Please help me.
Thanks in advance.