Title. I want a book about Brahma. It can be in the form of a Gita like Shiva Gita or Bhagavad Gita or it can be in the form of a Purana.
According to the Matsya-Purana (53.68-69),
rAjaseshu cha mAhAtmyam adhikam brahmano viduh : Meaning: It is said that in the Rajasika Puranas, the glory of Brahmaa is preached.
According to the Padma-Purana (Uttara-Khanda 263, 81-84)
Brahmanda-Purana, Brahma-vaivarta-Purana, Vhavishya- Purana, Vamana-Purana and Braahma-Purana are Rajasika.
According to some other opinion, Skanda, Padma and Agni Puranas are also termed as 'Rajasika'.
You could also read the Hamsa-Gita ( https://www.exoticindiaart.com/m/book/details/hamsa-geeta-text-transliteration-word-to-word-meaning-translation-and-detailed-explanation-IDK125/) which was told by Brahmaa taking the form of a swan. There are two Hamsa-Gitas by the way, the second one being a part of the Mahabharata and included in the Gita-Ganthravali by Satish Chnadra Mukhopadhyay.