I want to draw Data base design for postgres using features like reverse engineering.
So i want to know about various tools for drawing that are free of cost. Does any one have solution for this?

Check out MicroOLAP Database Designer for PostgreSQL.

It's not free, but you can can download and use it for a month on a trial license, and the personal use license cost isn't prohibitive...

It's handy for converting database from one system to pg, as you can reverse engineer the 'from' database on quite a few different platforms, then output the reverse engineered database to pg (either directly, or to an SQL file)