Allow me to chime in here, I agree that boys are your best investment. The orks work best when there are lots of them.
With that said, there are a few different builds that seem to work well in todays meta of 6th.
The first, (listed so as it is my preferred method) is speed freaks. Six squads of 12 boys, (one being the nob with boss pole and PK ) mounted in a truck with red paint, ram, and plank. Led by a big mek with KFF (displacing one boy from a truck until you get a burna boy squad). Two squadrons of three rockit buggies, and either a green baron (kopta with twin rockits and buzz saw) or a squadron of koptas. A good 1500 point list that will take on anything that can be fielded, and usually will win. When you get to 2k games a battle wagon full of burna boys is a great addition. Go to the ork boot camp thread and read the "Burna Boy Tactica".
The second, is the green tide. Five or Six squads of 30 boys, at least two of those squads are shoota boys, led by a boss with big choppa and attack squig (so he won't slow down his squad) and a squad or two of lootas and some grot kannons. It is a great hoot when your opponent says he doesn't have enough to kill all that!
The third, and a list I don't play but have a few fellow ork players who do, is the kan wall. Two big meks with KFF, two deff dreads, three squads of killa kans, and two or three squads of boys to fill out the points. When played right, it too has the potential to table your opponent.
The forth, and a bit pricey (points as well as money) is the rolling thunder list. Max battle wagons (eight are possible) with death rollers and grot riggers. Red paint is a good idea, and I like the four rockits rather than a kannon or boom gun. A wall of AV14 rolling across the board is a great sight to behold.
The fifth, and hard to win with but fun to play is the all biker army. It is harder to win with as it is like playing chess, you have to think out your moves and a single turn of bad dice rolling can send your chances of victory swirling down the drain. But, three or four squads of 10 bikers and a squad of 10 nob bikers, led by a warboss on a bike and our special character that makes bikers troops, is a challenge on many levels.
There are of course other mixed lists, and with practice, you can learn to use them to play well.
So, take a moment to decide where you want to go with the army. What appeals to you to collect, then decide what to buy. At any rate a few boxes of boys to assemble and paint should keep you busy while you make up your mind.