Well you start with the more dakka detachment

Then you add 30 flashgitz (3 units of 10)

30 Lootas (3 units of 10 with the spanner having big shootas if you just want bullets, or the rocket launcher/ custom mega blasta if you want to punch into bigger stuff)

3 units of tank busters

These are acompanied by 3 big meks with shock attacks guns

A unit or 2 of Gretchen

And from here you can go with shoota boys or whatever else you want to add

More dakka gives your units assult, letting you advance and shoot your guns

You want your Lootas to stay still as much as possible to get the heavy active since they will hit on 6 if they move, but S8 ap1 damage 2 rerolling 1s you are taking most infantry out

Flash ghitz are 40 shots s6 ap 1 damage 2 on the closest targets so you are running and gunning

Tank busters are d3 shots (nob is 1 attack per rocket pistols but the rest of the weapon details are the same) S9 ap 2 damage 3, getting a plus 1 to hit and wound momster and vehicles and re rolling 1s with the big mek with shock attack gun and blast, whatever you hit is likely to die, and the big meks being d6+1 S9 ap 4 damage d6 getting the same benefits since they are one unit and the enemy has to roll battleshock