I was planning to build a new chassis as the one I have got a bit bent. But I can't find my book.
Does anyone know where to get a pdf version (preferably free )

Closest option is the mcsorley plans, they can be downloaded. There's a few bits missing (transmission tunnel for example) but the bulk of it is there.

thanks thats what I need.

Ron Champion or Chris Gibbs Haynes book ?

Ron Champions book, are the chassis different?

Yes they are quite different. The Gibbs chassis is bigger in nearly all dimensions to accommodate unmodified Sierra bits. The Champion is small and better proportioned (IMO), more suited to live axle or de dion setups. The Champion is the Locost, the Gibbs is the Haynes Roadster.

Sadly BOTH have poorly thought out suspension.. in mountings and layout.
Take a look at the much maligned Caterhams as a reference for what "should' be built.
But Hey! why quibble. These DIY's are essentially Poser builds :-)