With Sorc Shoes anywhere in between chalice and DFG. Depends on how the game is. Sometimes I'll get voidstaff before Deathcap if I feel like I have enough AP and am gibbing my main targets already. Anyways, another option is to get Kage's, then get Catalyst and get a RoA before Deathcap. Whatever you do, don't do Archangel's. Tear isn't that good for you and you REALLY don't need the AP from it, you'd be better off with items that give you more utility.
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i usually go
boots + 3 health pots to start with
kages lucky pick which you build into DFG
upgrade boots into sorocer shoes
Rylais if needed more hp or slow OR Void staff if they get lot of Magic resist OR Zhonys Hourglass if needing armour/invunrabilty OR Abysal Sceptar if needing Magic resist
then just get rest of items that you didn't get above this builds focuses on getting veigar a lot of ap while making him a bit mroe tankeir where he needs to be