I have never made a guide before, but this is the build that I currently have for Ezreal. I had never gone mid before either but in 2 separate matches I went 13-1-13 in the first and 21-3-12 in the next.
In this build I go attack damage for a few reasons...
#1 His passive supports it with increased attack speed
#2 His Q applies on hit effects and scales with AD
#3 He is an underestimated champ who can hit hard with Basic Attacks

Personally I only have 2 Rune pages, 1 for AD DPS and the other for Mage's. so I have
9 Greater Mark of Desolation - 1.66 Armor Pen
9 Greater Seal of Alacrity - 0.76 attack speed
9 Greater Glyph of Celerity - 0.05% cooldown per level
3 Greater Quit of Desolation - 3.33 Armor Pen

I haven't experimented enough with other Masteries to see what would benefit the most.

-For Items I take mana crystal first so you can use your Q much more to wear down your target for a gank.

-Build that into a sheen as quick as you can for more mana, and your Q will hit much harder.

-Next go for a tear of the goddess so you can say goodbye to your mana troubles.

-I go Berserker Greaves next for the extra attack speed but you can take Mercury treads if you prefer.

- After shoes I can't recommend enough the need to rush your trinity force. It will make your Q hit like a truck and any other attack you make.

- With your Q hitting hard and basic attacks a source of sustainability is nice, so I go for a vampiric scepter.

-Next I go with the manamune because it will be built up nicely by now, especially if you spam your abilities like you are supposed to.

-Bloodthirster will give you great life sustain as well as beefing you up even more.

-Infinity edge is the best AD item you can get cause it just makes you hit harder all around, only downside is its freekin expensive.

-The last Item I havn't quite decided yet because by now you usually win. some suggestions would be Last Whisper for Armor Pen, Phantom Dancer, Madreds Bloodrazor, or a defensive item.

I would always recommend starting with Q first. It has a relatively short cooldown so you can poke your opponent whenever possible and you can use it to last hit minions. Max out Q as quickly as possible so you can spam and do lots of damage quickly

Arcane Shift is the second ability, with it you can leap tall walls, and it is great for last hitting champs in a teamfight. (By the way I do not support kill stealing)
Practice jumping walls because it will save your life almost every time. And if they chase with flash, you can flash another wall. If they still chase you should be able to delay till your cooldown allows you to jump yet another wall
My main tip is if you must venture a little ways from your tower, make sure you have enough to escape should something go wrong

I choose to get 1 rank in Essence flux for a few reasons.
#1 It will help build up your tear of the goddess
#2 It's debuff with hinder your opponents farm and it will pass through minions.
#3 It's buff will stack your passive as well as benefit team mates in all cases
Those are just a few benefits. Also realize that it will pass through minions so you can use minions for cover and poke your opponent

Finally the Ult
It is a very nice ult because it travels across the map and can be used to snipe last hits from those who think they are home free.
more than half the time if i cannot get to a tower to save it from enemy champ hits, it will scare them away long enough to save the tower. (some people instinctively move towards something even if it will hurt them. I've seen it many times)
Also you have to decide whether you want to use it at the beginning of a teamfight to damage everyone, or wait a bit to try and pick up a kill with it. I've gotten 3 kills with one because I was late to a teamfight, but don't count on it.
Lastly in a very desperate situation, it can be used to last hit Baron Nashor and snipe it for your team. I've only seen it once, but it is possible.

I have lately been favoring exhaust and flash as my summoner spells.
-Exhaust can be used to chase down an opponent for the kill, or used to escape. I have also used it on a Tryndamere surrounded by minions to chase him from my tower.

-Flash can be a lifesaver when your arcane shift is on cooldown. Essentially a double flash can save your life, or get you enough distance to get the kill.

-Promote is a nice spell to have when you have no idea what your second should be. It can help you push a lane, or late game, you can send a super minion down the lane while you go elsewhere to farm or help teamates.

-Ignite is good for the last bit of HP, or if someone has a heal up their sleeve.

I'm sure there are better things I can do with this guide like add pictures, but this is just suggestions and it is by no means a requirement for anyone. If you would like to comment, please do but please no negativity.
Thank you for taking the time to read my first build, and happy Ganking.