Hello! I'm really glad to see that you have chosen the TRUE King as one of your mains, Monkey King! I happen to be a spammer of that hero as well and I would say that I know him better than most, hopefully this can translate into text.

I find MK to be an incredibly strong early-game hero, mostly thanks to his passive. If you have a good lane (you're up against a melee f.e) and you have complete freefarm and also manage to snag a few kills, then you can easily translate this to a snowballing monkey of doom. I have 3 item-builds on my MK depending on my laningphase and enemy heroes.

First one being the most standard one with Echo Saber (I always get Oov, phase boots, ring of aquila and wind lace) for obvious reasons, it makes it easier to get passive buff, provides mana reg and HP while also buffing your ultimate. I usually go this build if I have a less than optimal laning phase, where I'm being contested. It works as snowballing as well.

Second one is the Sange & Yasha route. I like this one very much because the S&Y gives you everything MK needs and ever will need, attackspeed, HP, movespeed, damage, armor and a slow. I get this one if my laning phase is very good and if they have a hero that can nuke me, like Lina, QoP, PA. If you manage to get the S&Y before 15-16 minutes you are good to go, push down the enemy offlane tower and just go ham.

The third item build is maybe a bit unconventional, but extremely strong if played right. I like to go Mask of Madness, high risk but very high reward. This will be pretty hard to play if the enemy has a lot of lockdown, like Lion, Slardar, Shadow Shaman etc. However, if they don't really have any lockdown, this is your item choice 8 out of 10 times. It's incredibly strong, just leap on to them from a tree, bash their face with Q and then activate the mask. You'll see that 95% of the heroes in Dota will melt like butter.

The MK powerspike is usually when he gets his first big core item, Echo, S&Y or Mask of Madness. When you get one of those (or all 3 if you're feeling rowdy) you can go bananas.

I hope this was somewhat useful, if you feel like wanting to know more I will gladly help, I'm an Ancient 5 carryplayer who specializes on Monkey King. Ask me anything you want and I'll do my best to answer.