How many abdominal sclerites would be there in a cockroach?
Tergal plates:

There are ten tergal plates. The $8^{th}$ tergum in the male and both $8^{th}$ and $9^{th}$ terga in the female are not visible  as they are overlapped by the $7^{th}$ tergum.

The $10^{th}$ tergum extends beyond the posterior end of the body and has a deep groove in the middle of its free end.



Sternal plates:

Only nine sterna are present as the $10^{th}$ sternum is absent.
In the male, nine sterna are visible whereas in the female, only seven sterna are visible.

In females, the $7^{th}$, $8^{th}$ and $9^{th}$ sterna together forma brood pouch. The brood pouch has two parts: the anterior – genital chamber or gynatrium  and the posterior – gothecal chamber.


(source: lander.edu)  


(source: lander.edu)  




Sources:


http://www.slideshare.net/prof_aarif/animal-types-cockroach
https://learnzoology.wordpress.com/category/periplaneta-americana/page/15/
http://zoologybaburao.in/pdfs/7.%20Unit%20VII.pdf (Best)
http://www.eskool.com/files/subject/ppt/103_11_07_04_01.pdf
http://www.sakshieducation.com/(S(clpea355rwddux55iuci1cer))/Inter(New)/Material/IstYearEM/Zoology/07_01_ARTHROPODA_COCKROACH_UPTO_LOCOMOTION.pdf


Update:

Youtube links for Cockroach dissection:


https://youtube.com/watch?v=ZwvG69ICnps
https://youtube.com/watch?v=wF7ew2w24as