What do you build for AD Lulu?

I think a build similar to Kog'maw's would work pretty well. This includes:

I wouldn't bother building AD on Lulu.

If I wanted sustained DPS, I'd probably just grab Nashor's Tooth on her.

You don't build AD on her, you go for attack speed on-hit items so you can auto attack faster, therefore applying her passive more often. Something like Nashor's, runaan's, BoRK, Greaves, etc. I wouldn't bother with sheen items such as trinity force or IBG.

If you actually do mean AD and not on-hit, then I assume your build would just be the typical ADC build. BF sword>PD/Runaan's/Shiv>IE/ER>Greaves>BT/BoRK>LW>GA/Banshee's, though I wouldn't recommend this as ADC Lulu really brings nothing special to the table.

alt+f4

depends do you really mean AD, or do you mean autoattack dps?

Basiclly any ADC build tbh xD