The DOTE in Chennai has historically published "Polytechnic Series" books for Tamil medium students. You can find these on:
are available on the Internet Archive, providing specialized knowledge on engineering drawing and site work. Internet Archive Independent Academic Portals diploma in civil engineering tamil medium books pdf
Not every subject has a free PDF. If you cannot find a specific book: The DOTE in Chennai has historically published "Polytechnic
The most reliable source for official textbooks is the Tamil Nadu government's educational websites: diploma in civil engineering tamil medium books pdf