BUILD :
I always want to go with glacial whether im AP or AD, since it's very cost effecient. You dont need to upgrade boots before you get BOTRK, unless you play against an AP or AD threat, that you need some resistance against.
(You can also go early ionian boots for full cdr)

Then i really love to build Deaths Dance on ezreal, since this gives him some extra survivability and some extra sustain, compared to mercurial scemitar and Maw, and also fills the cdr cap if you went merc treads or ninjas.

Then i get bloodthirster for my last item, but you can swap it out for qss.If possible i sell my shoes for black cleaver and get the HP and tenacity elixir.

And thats the most op marksman ever.

When you max your q, the damage will only increase slightly and the cooldown goes from 5.5 to 4.5 at lvl 5. however if you max e you will be way more slippery, have more flat damage for burst (together with w) and still have damage on your q.

you will be way easier to gank, since you dont need items to do damage, so make sure you hit your w, before following up with e.

I prefer to max w after e, but if you need to kite in teamfights, you wanna put 3 points in q, before you start maxing w. (You can put 3 points in q, if you're getting shoved in early, since this will give you better waveclear)