i got fg thinking about putting a sub in just wanting know what size sub would fit in the parcal shelf ?? or should i just got with 12inch sub in the boot

come on some one gotta know ?

Depends what you are looking for mate
Installing a sub in the parcel shelf is a big no no, it is pretty common for them to push enough air to break your rear window.
I have my 12inch subs mounted in the boot, I had to make a custom mount for them, but it's pretty tight in there and standard boxes don't fit