what are the best books for nata and for maths questions which book should we refer?

Here are some of the preparation books you can prefer for NATA.

• Architecture Entrance Book- P.K. Mishra
• A Complete Self Study Guide for B. Arch Entrance Examinations- Arihant Books
• Engineering Drawing - N.D.Bhatt and Pancha
• Verbal & Non-Verbal Reasoning Book- R.S. Agarwal
• NATA & B.Arch Question Bank  by Ar. Shadan Usmani
• NATA & B.Arch complete self study material: entrance examination by  Ar. Shadan Usmani
• A Complete Self Study Guide for B.Arch by P. K. Mishra
• B.Arch Entrance Examination Guide by Surendra Kavimandan
  Arihant M.P Mishra Barch Book.

Hiiii

B.Arch exams comprises of Perspective drawing, 2D, 3D and aesthetic sensitivity test. So there is no ideal book from where you can learn and the questions have no fixed pattern as they keep on changing. So don't just refer one book but, go through all books (or at least as many as you can).
Here is a list of few excellent books which you can use.

• NATA & B.Arch Question Bank  by Ar. Shadan Usmani
• NATA & B.Arch complete self study material: entrance examination by  Ar. Shadan Usmani
• A Complete Self Study Guide for B.Arch by P. K. Mishra
• B.Arch Entrance Examination Guide by Surendra Kavimandan
• The Young Architect by Neelam Verma. The complete book for B. Arch. entrance exam preparation.
  

For mathematics here are some good books.

• Higher Algebra by Hall and Knight
• Coordinate Geometry by S.L. Loney
• Differential and Integral Calculus by N. Piskunov
• Calculus and Analytic Geometry by Thomas and Finney
• IIT Mathematics for JEE Main & Advanced by M.L. Khanna
• Course in Mathematics for IIT-JEE by Tata McGraw Hill publication
• Problems Plus in IIT Mathematics by A Das Gupta
• Trigonometry by S L Loney

Also i will suggest you to keep on solving the sample papers and previous year papers so that you get the idea of how the paper is set.

Prepare well and do good.
All the best