MegaNobz and nobz are elites
Nobz aren't really good tho.
I would suggest mega nobz in squads of 3 in a trukk (so that would make your next buy 2 trukks) They can't ruz cuz of their mega armor, making them really slow if they aren't in a transport.
You can add 1 Nob with each squad of boyz.
So take 11 boyz and 1 nob with a bosspole and powerklaw all in 'eavy armor and in a trukk (if you want your boyz in trukks)
I would suggest another 5 loota's. (the box give you all the weapons and heads for burnas so with another boyz box you can make some burnas, problem is they aren't anny good.
take some bikers. 6+ bikerz are good, specially if you fit a painboy on a bike.
Make some mek gunz. there is a youtube video how to make 4 mek Guns from 1 mek gun kit and 1 trukk kit (save you a lot of money) an maby buy some extra mek gun bitz on ebay of an online bit store (i got some of the armor plates, chasis and random bitz + grots from ebay and made 5 mek gunz from 1 kit + a trukk kit and some bitz i got in my bitz box)
and i would take more Boyz. maby 10 or 20 more.
My List for 900 points is something like this:
hq: Painboy 9with more point i take a warboss instead)
Elites: 5 tankbustas in a trukk with ramm (2 of these)
Troops: 11 boyz + nob with bosspole and powerklas eavy armor in a trukk with ramm (2 of these)
or 19 boyz + nob (+ the painboy) and 10 gretchin
fast:
5 bikers + nob with Big Choppa (2 of these)
Heavy: 5 Lootas
1 Kustom mega cannon with 2 extra grots and 1 ammo runt (2 of these, or i take 5 extra lootas instead of the mek gunz)
With more points i just take more taknbustas or mega nobz
more boyz
More bikerz + warboss and/or painboy on a bike.
More lootas
I personally really like the painboy. for 50 points (75 if hes on a bike) anny unit get an extra 5+ save.