No you cannot.
Yes, but you have to be online to make one.
I mean, like how do you get to the option to make your own class? I do not have Xbox Live. Do I need it?
no , but call of duty modern warfare reflex (cod4) has
no...
I Just reach lv 5
If you are in a private offline match, yes, you level up just like you do online and you will unlock the class customization at level 4.
You cant exactly make a gun in black ops, but you can customize a gun in multiplayer create a class mode and play online (or offline) with the customized gun.
Do mean how do u get the grenade launcher? Cause theres no RPG assault rifle on cod4. If so you need to unlock it by completing that specific guns tasks e.g. kill 100 people with that gun. Once you unlock it go to create a class and select that gun and choose the add-on you want.
you have to get 150 headshots with all of the guns in that class. Eg: Get 150 headshots with all the smg and then you will get a golden mini uzi
it should be level 4 at least it is on black ops
cod4 for sure
google and look for cod4 1.7 updater