help me make my gift printable

I got this model I want to be printed in silver.
I dont want to sell this, its going to be a special gift for my close friend.
I've never used Shapeways before.







I have few problems now. The volume seems very low and I get a warning that the walls are too thin even though I've made them 0.8 mm as suggested. Any ideas whats the problem?

Help me by telling me how to change the model to make it printable in silver.
Thanks!

Hi.

PM sent

Regards

Luis