The phrase "becoming a common" is correct and can be used in written English.
For example, you could use it in a sentence such as, "The practice of sending Christmas cards is becoming a common tradition."
Analysts say the Kawanos' story is becoming a common one.
The Polski sklep is becoming a common sight on the British high street.
Momentary dreams for many United opponents are becoming a common headache for Alex Ferguson.
"In talking to police chiefs all over the country," he said, "it's becoming a common problem".
Instead, in what is becoming a common political strategy, officials outsourced their displeasure to the mob.
"And we're now at the stage where digital plumbing is becoming a common component of the infrastructure of new homes".
Indian market regulators are facing what is becoming a common predicament in emerging markets: too much money.
More quietly but more significantly, other means of distributing information were becoming a common part of life.
But the undercurrent was the same: labor disputes are becoming a common feature of the Chinese economic landscape.
It's becoming a common thing.
The hair dye poisoning is becoming a common suicidal poisoning.
