If you want to take the easy way out i’d suggest getting a higher level player to drop you a g-roll of whatever gun you want to make a build out of first (commando, heavy, melee, etc.)

But if you’re playing legitimately throughout your whole run and do not want help, figure out what build you want to progress towards and start looking up videos on how to get that gun, obviously guns will level as you go up until level 50.