I attended an adult build in February. Most of the people just came to collect the parts and left without building it there. While we were building ours, the staff gave each of us an older poly bag also.
I want to participate in these builds in the hope they will continue to offer them. Since I don't know any adult builders, I hope to meet some at the adult builds.
I am signed up for the 3rd of 3 building times offered at the store where I shop. Lol, my excuse to get back to a LEGO store. :-)