Translation:Shall I make something?
The ～ましょう form can function in many ways. It can 'imply doing something with another person' just as you mentioned, yet it can also imply the speaker's intention (as in this sentence), and it can express commands (in an indirectly way) and predictions of the future or guesses to things.
I think its because 何か is used for what questions in general, and を for things that are physical direct objects of something. I think if you used 何を you'd be talking about two or more previously mentioned subjects, as in 'which one shall I make?'
But that's just what I instinctively think, so please correct me if I'm wrong.
these are confusing, sometimes it's "would you like me to ..." sometimes it's "shall i ..."