Book On Comparative Study Of Four Schools Of Thought
If you are looking for the history of Fiqh and its evolution into four famous madhabs then Book by Bilal Philips is a good start ( Attahed here ). And if you are looking for comparative fiqh on major topics including purification, Prayers, Zakat, Fasting and Hajj etc. then book ‘ Fiqh-us-Sunnah ‘ by Sayyid Saabiq is very famous and can be referred to for gaining brief yet complete insight on these topics ( Attached here as well ). But in order to gain comprehensive insight into comparative fiqh, one is advised to refer to source books and not rely on any third-party work in this regard.