This guide is to help you get an understanding of how to build a proper damage heavy Hecarim, you CAN do this from a jungle perspective however I find it much less successful as a top lane Hecarim gets much more gold easier and this build is very snowball-y.
Ghost is very useful to Hecarim whether disengaging, engaging or brawling, always have it. TP is very useful for strong ganks and flanks throughout the game, but isn't necessary because you can run back to lane very quickly. If you don't want TP; Flash, Exhaust and Ignite are all good options to meet your needs.
Try to harass melee champions in lane in the very early levels with your q spam, but make sure not to run out of mana. You don't have to be too afraid of ganks because of your E speed and ult just don't die 1v1 and if you think the enemy is gankable ask for them because hecarim is a very good person to gank for, especially post 6.
Later in game try to run into the enemy back line as standard Hecarim, but get out before you get bursted down since you won't be able to stand against the punishment. Don't forget to q as soon as your E hits the target for some free damage.