Pretty basic Tank with an AD Focus Blitz sitting here. No surprises or anything really. it works, make sure you solo lane top with him, and it is a preferable pick if he will be in a 1v2.

Since the focus in this build is your AD (from increased attack speed from Overdrive as well as doubling the damage with the Power Fist), Armour penetration Marks make the most sense. You are going to either Tank or be Tanky (depending on how you want to execute this build), so the Magic Resist Per Level Glyphs and Armour Seals make sense too.
As Blitzcrank, your primary job is to land pulls from Rocket Grab and Popups from Power Fist. MS Quints make your ability to get in range/position for solid pulls a lot easier.

Blitz wants to have his pull first in order to be ready for a supreme push of the top lane if it happens, or if your team decides to try to steal the opponent's blue buff, or defend your own, the use of the pull in a teamfight is better than either of his other two abilities.
Next you get the popup for the pull/popup combo that he is notorious for. This allows for you to kill anyone that comes too close to your tower with incredible ease.
Level 3 you want Overdrive in order to make your positioning easier and to make escape from sticky situations easier.
I max Overdrive first because the rest of his moves scale quite poorly for what you want them to do. when levelling up his E, the only thing that is changed is its cooldown. and on his pull, you increase his magic damage from it. these things are nowhere near as useful as an increase in the speed buffs of Overdrive. with those buffs, you will increase your damage output as well as your survivability.
After you have maxed Overdrive, it doesn't actually matter what you do, as long as you get the final rank of your Ult at 16. the other abilities have equal value in their upgrades in my opinion. Generally I lean more toward upgrading the grab though, because it will increase my burst damage, whereas upgrading the Power Fist, I will only upgrade my damage over time.

Flash is Flash is Flash. it is the best summoner spell in the game, even with its nerf on range. It gets you out of the worst situations and jumps you in when you need to. its perfect.
Teleport is a key spell for nearly any champion that plans on being in the top lane solo. It allows you to seem to have Omnipresence, and the ability to, out of nowhere, heal all of your health, mana, and even buy items, after having only been gone for 10 seconds.

My Items mostly focus on Blitzcrank's passive, as I quickly get Tear of the Goddess. Because of the quick cooldown on Power Fist, and the ability to overuse Overdrive, Tear very quickly reaches its cap of 1000 bonus mana, causing you to pretty much never run out. Manamune ends up being key in your AD aspect, and Trinity Force just perfects that to make you a threat while in teamfights as well. Force of Nature allows you to Initiate with a Pull/Popup combo, Overdrive away once you have been forced to activate Mana Barrier, then wait a second and Overdrive back in with most of your health returned. The Passive on Frozen Heart will make you seem like the better of two AD champions, and cause others to never want to 1v1 you, as well as give your team the upper hand in teamfights. Oh and it gives a ****load of mana. The last Item is subject to any change necessary. Banshee's Veil is there because it provides mana (of course), and Health, which was somewhat lacking in the rest of the items. and MR kinda helps.

tl;dr - Get Tear/Manamune and use Overdrive all the time. attack alot. kill towers. be tanky. win.