Gregory is correct with the dynamics and complexity. That's the reason why we adress this with our module WPA.
http://www.ptc.com/product/windchill/product-analytics
Weight is not fully OOTB right now, but we do the BOM rollup for Cost. There is the option to have custom logic which will do the same for weight.
What is your business use case behind this requirement? Is your customer designing huge machines or plant pieces which he needs to transport later on? Design to cost and weight has a great potential to shorten design cycles since you do it right at the first shot and you can directly identify the parts with biggest impact.