I am interested to learn more about Shiva.
- What are the Puranas to follow?
- Apart from Puranas, are there other works which are authoritative and talk about Shiva?
- Are there any epics which have Maheshwara as the core subject?
The story of Shiva is as the name suggests covered in detail in Srimad Shiva Purana. Srimad Bhagavad Mahapurana also entails various leelas of Shiva. Srimad Devi Bhagavatam covers episodes of Shiva's glory relevant to Devi - Sati, Parvati, Kali. Linga Purana is also detailed narration Shiva and his glories and why we worship him as a linga. [This aspect is also covered in Shiva Purana]. Kalika Purana the story of Kali Maa and Nandi Purana the story of Nandi may also be read.
There are also episodes of Shiva covered in Srimad Valmiki Ramayana and Srimad Mahabharata but most information is available from the first three puranas mentioned above.
This list may not be exhaustive, and is to the best of knowledge. In case there are other scriptures, the same may be added to this list by the learned readers who can edit the answer.