Phy file problem

Hi there I got a problem. I edited a model from the SBMP and now its works under Gmod but i cannot walk on it so i checked and i need to make a .phy file. The question is how do you make them?

Thank you

EDIT : I got the phy file now but its not a the good place (collision)

EDIT #2 :The collision is at the right place but is full and i cannot walk inside the props.

That picture doesnt help at all. Type vcollide_wireframe 1 in console and then take a screenshot

Also: http://www.hl2world.com/wiki/index.php/Complex_Collision_Models

That was before… I fixed the location now the problem is the collision is full and I cannot walk inside the model.

EDIT : The link you sended me provided me some information about my problem thanks.

You need to make the collision model and then compile with “$concave”.

Yeah i know so its done my model works and collision too thanks for those who anwsered me.