TOPIC: "The two shirts are much of a size."?

"The two shirts are much of a size."
I know the above sentence means the two shirts are similar in size, but I don't know how to use "much of" exactly. Would you please make clear it with an example.

In your enquiry you ask about hte use of "much of."
The sentence," The two shirts are much of a size,"does not make any grammatical sense. In Fact, I find it hard to understand the meaning. I can assume, as you do, that it means they are both similar in size.
In order to use "much of" you would need to use a non-countable noun in a sentence such as,"much of the information we gave them was young"

Regards