Hi Bertier.
The Cutlist plugin could do what you ask but it would need some modification of course to do everything.
It already computes volume, so if your model was made from the same type of material, then it's a simple matter of multiplying.
If your model is in metric units, then it computes total cu.m. If in imperial units, it displays board feet.
If it was composed of different materials with different masses, then of course you need a way of assigning weights to either the material or each component.
I always imagined using custom attributes. I will need this for other things as well, for example for grain orientation for the layout function (since Sketchup has no idea about this). Other attributes which would be useful would be cost of material.
Then you could either add the cost, weight, etc back into the description or simply output as part of the materials list output In either html or csv output)

But, of course, only the first part is there without modification and I currently have no plans to made modifications for a short time anyway. It is nearing summer here and now I need to so some projects in the real world - in the shop!

Steve