What are good books on the topic of seerah of Umar bin al-khattab?
The best book I have found on Umar’ life is this one compiled by Atif ibn Abdul Wahab ibn Hammad which is called Jami’ Al-Aathar al-Qawliyyah wal-Fi’liyyah Saheeha Li Ameerahul Mumieen Umar ibn al-Khattab. It consists of more than 1000 authentic narrations! It is only in Arabic here
He has also written one for each of the Khulafaah (i.e. Abu Bakr As-Siddeeq, Umar bin al-Khattab, Uthman bin Affan, Ali bin Abi Taalib). Very Beneficial
Faisal Ibn Abdul Qaadir Ibn Hassan