Obviously, you would jungle with Hecarim, so smite, you can also get flash instead of ghost, but you can blow ghost during fight for ad boost. You can also use ult as replacement for flash. Teleport and ignite is useless, because you have to much mobility, it's not worth it to teleport, as opposed to other, slower champs. Ignite would rarely be used to pick up escapees, as Hecarim is fast and sticks to them, you also don't need the ad and ap it gives on cooldown (with mastery), you also have burn from Elder Lizard (both item and buff).
Items are pretty obvious, while I see the better Hecarims go tanky instead of speed, I like this build because Hecarim's one of the few champs that could use Zephyr, and because it gives tenacity, you can get Swiftness instead of Mercury Treads. The starting items, hunter and five pots are pretty obvious (you can't do anything else (not even boots), Hecarim relies hunter's +10% on his q, and because he as rather high dps, he can use the 10 true damage, then he needs a lot of pots, his w isn't enough for sustain). The obvious enchantment is furor, and you need an item that builds off sheen. I personally don't like ice-born, you create a field, then knock them out of it. Also, it's generally for maramana users, and this builds already gives enough cdr, and if you only spam q, you'll never run out of mana with Elder Lizard, so Tri-force (it gives movement!). Of all the movement speed actives, I like BORTK the most, it also gives essential life steal and because you don't have ice-born, you need another sure-fire slow (don't forget you have phage). And because you have another attack speed item, you can make more use of the passive...and at the end, more movement for your passive. Elder Lizard is pretty much your core item, the mana is burn is important for your q. Your last item can be whatever you want, I would get GA, then sell it when it's on cooldown for an hp item (warmog, randiun, sunfire).
The only thing questionable with the masteries is the three points on attack speed. Well, because Hecarim doesn't need dps or cdr, you can get 3 points on any, and 3 (instead of 2) on havoc. You get dps for early game machete.