Hi Pal,
Commercial valuation is relativly easy but the angles to make money are much harder.
You only need two books but you can add one more for reading when you have got a grasp. DO NOT GO ON ANY COURSES it is a different world to residential.
1. Modern Methods of Valuation - this book is required material for all students of real estate- will teach you everything you need to know about "proper" valuation
2. Parry's Valuation Tables (13th Edition) this is a book full of tables and charts. It is the bible of valuation It would be impossable to use book 1 or value anything without it.
Both these books are available from the Royal Institute of Chartered Surveyors website. Total cost around £35.00