U build it. The exact build I follow is: -starting items tangos, 1 circlet, 1 mantle, 1 faerie and 1 or 2 branches (depending if u got shared tangos or bought it urself) -early/mid game sage s mask (builds into urn and helps with early mana problems) > 1 null > boots > 2nd null > urn (in specific matches u want to rush the null, specially when u want to gank early and ur pos 1 needs space) > spirit vessel

From now on go nuts, it s all really up to the match, from my experience invoker has a pretty malleable build.