Is there any reference for equivariant RiemannRoch formula: book, paper, notes or something? I want to compute the weight of the action of C^* on the top wedge of cohomology group.

You also have some lecture notes on the web page of Michel Brion here. This paper of N. Berline and M. Vergne is well written (but is more "Lie Group theoretic" than the previous references and it is written in french...). 


You could try one or all of these (same authors): Dan Edidin and William Graham: Algebraic cycles and completions of equivariant Ktheory here RiemannRoch for equivariant Chow groups here Equivariant intersection theory here 

