Welcome to Librarium Online!
So far I have 16 boyz, 2 burna boyz and 3 mega armored nobz what should I buy to beat the monilith
Firstly I'd try and get a playable army. Remember you need a HQ and two troops to have a battle. You'll need a Warboss and more boys before your army is legal.
Secondly your forces are currently so small, it's unlikely you'll ever play a Necron force large enough to have a monolith, worry about it when you play bigger battles. Your getting way ahead of youtself
Thirdly, you shouldn't be focusing on trying to destroy one particular unit - you should be trying to write a "tournament style" list designed to take on all comers. Design a list to take on Eldar, SM, Nids - not a Necron killing list.
Finally, Orks really don't do very well against the Monolith anyway. Zap guns are probably the best method and they are very unreliable. The real way to beat the Monolith is through "Phase out"...
me and my friends are going to play 1000ish point games. my friend has the nightbrigner, monolith and warriors so he can play I'm getting a war boss soon so I can and my other friend playing as chaos marines has 30+ random units and he can play. i'm going to get pwn'd
Well if your friend brings a Nightbringer and a Monolith, that's very good for you.
Let me explain how Phase Out works. If the Necron army is reduced to 25% of it's original number of models you automatically win. Only certain units count for being for Phase Out - those with Necron in their profile (those that get WB - the Monolith and Nightbringer don't.
So by investing so many points in units that don't count towards phase out, all you have to do is target those units that do (which he shouldn't have many of because the Monolith and Nightbringer are so expensive) and you should win, without having to kill the Nightbringer or the Monolith.
I wouldn't worry about how many models your friends have, as playing with equal numbers of points means the game is balanced. Just make your army legal by getting another box of slugga boyz and a HQ and the rest will come later.