The first time i played [olaf] i was bad. But now that i have this build i own top lane every time. A few reasons were to blame i was bad at the start. One of them was not knowing this build.

i find that for me it is more fun (and is a bit cheaper) to have that little bit of ad on your quintessence's instead of hp. but that is up to you. For Marks i went attack speed instead of armor pen just because it will help you get a first blood more easy or if you want to jungle a faster time. for your seals you really need magic resist because i don't really have any of it in the build.

i normaly get [exhaust] and Teleport for you fights top 1 on 1 or you can take ignite for a top like volibear, warwick or Dr. Mundo again for getting easy kills. But you can skip the teleport to get the other one.

to start you always get a doran's schield it gives you a lot of hp and health regen and some armor. then your boots you can get the ninja tabi or the merc treads but you have your ulty so don't worry about stuns and just get the berserker's greaves. They are almost every time my choice. the frozen mallet is everything you need a slow good amount of hp and some ad. atmas impaler is very important it gives you armor and a lot of ad later in the game. Warmogs for the hp and for the ad thanks to your atmas. I used to get starks but they changed it into zeke's herald. It helps out the real carry's and get you the life steal. your last item is up to you most of the time i get a black cleaver but i sometimes go for a banshee's veil for the magic resist.

get your undertow maxed out as fast as possible it will be your main hurras. If you are in a 2 Vs 1 lane you need to try and hit them at the same time or focus one down so that your jungler can get you some kills. if you are outplayed bye the other team and need some hp activate your vicious strikes and then your unthertow on as many minions as posible it wil recover about 120 Hp at lvl 5. And if you are able to push your land don't be careful at lvl 6 but alway's keep mana for your ulty so that if they come to gank you can just run away with little hp lost.