So why not just make Wit's a big ticket item?
Like, really big ticket.
UNIQUE passive: Your basic attacks deal 4% of the target's maxium HP in magic damage OnHit.
UNIQUE passive: Your basic attacks steal MR from the target, stacking up to 5 times.
UNIQUE passive: Your basic attacks (and all OnHit effects) deal magic damage rather than their normal damage type.
Boom, relevent.
, you clearly need to get some armor...so you go ahead and buy
and
5 minutes later she buys a wits end and uses the toggle...completely negating 5000 gold worth of armor you just got and forcing you to buy a bunch of mr, but, unlike most switch builds, (like say ad/as kayle selling some items to buy a deathcap/rageblade), you have to keep the armor, cause if you sell it to buy mr, she can just toggle back to physical.