Are they ok?
(in a pub etc.) If I say like this,
I'll have a coffee.
I'll have a beer.
I'm gonna have a coffee.
I'm gonna have a beer.
Are they ok?

Question

Are they ok?
(in a pub etc.)  If I say like this,
 I'll have a coffee.
 I'll have a beer.
 I'm gonna have a coffee.
 I'm gonna have a beer.
Are they ok?

Answer

When placing your order use "I'll have." 
"I'm gonna have" sounds like you are talking past the waiter, and not directly to him.

Answer

Perfect