Welcome to Librarium Online!
Hi guys this is my first ork army list so tell me what you think
DA DEMON UNTERS LIST for the orks
WARBOSS - Big choppa , twin linked shoota, eavy armour = 75pts
NOBZ - 4 Nobz with - power klaw, stick bombs, twin linked shoota, eavy armour = 116pts
BURNA BOYZ- 5 burna boyz 1 mek = 75pts
ORK BOYZ- 15 boyz with sluggas and choppas 1 Nob with big choppa 1 boy with big shoota = 110
ORK BOYZ - 10 BOYZ with shootas and 1 nob with power klaw = 85pts
TRUKK- armour plates = 45 pts
The warboss needs a powerklaw. Marines and monstrous creatures are just going to laugh when he attacks if he can't deny them their armor save.
I wouldn't use nobz like that. It costs the same as a full squad of 12 boyz (for a trukk) with only about half the benefit. When using nobz, you should use 8-10 with 2-3 powerklaws, painboy, cybork bodies, waughh banner, bosspole and trukk. Anything else isn't going to outperform normal boyz. Most of the advantage of nobz is how well they survive. Without a painboy, cybork, numbers, bosspole and a transport, they just don't last. 1-2 rounds of shooting, and they'll be gone, even if the warboss is attached.
The burnas are alright, but they need a transport, either a looted wagon or battlewagon, or they won't survive past turn 1-2, and have literally no hope of hitting anything with their burnas, unless your opponent doesn't understand what they are.
For regular groups of boyz on foot (no trukk) you need at least 20 in the unit, and again, you need a powerklaw, or you'll have virtually no chance of ever beating a space marine opponent. If you're going to use orks then you need to use powerklaws, or else you're not going to win. It isn't optional.
To save points, you could always just not give one of the units a nob, and instead attach the warboss. This can work, as long as they have a powerklaw and bosspole in there somehow.
Don't put armor plates on a trukk. If the enemy can shoot it, and it isn't at least obscured, it's dead. If the enemy has a way of getting a direct hit, it's gone. Keep it out of sight until you're ready to use it. Armor plates aren't going to make a difference. They're just too easy to kill.
Here's how I'd play the list:
Warboss with powerklaw, cybork, 'eavy armor, bosspole 
20 slugga boyz w/2 big shootas  (attach warboss, and use nob figures as boyz)
12 Slugga boyz in trukk w/nob, powerklaw, bosspole 
5 Burna boyz 
Looted wagon w/big shoota  (you could use any 40k vehicle for this)
If nothing else, trust me on the powerklaws. Good luck!
"Any job worth doing, is worth doing with a powerklaw."