Hi, is it posible to make custom Cod4 maps using Unity3d ?? That would be great if i could 
No.
No and why would you? Cod4 level editor is perfect for FPS level design, much better suited than any engine out there. Clip brushes give you full ability to create levels without much need of external tools like 3ds max or similar.
No.
COD utilizes a special game engine, and people outside of the artists at Infinity Ward cannot use it. That means unlike other games, you cannot create so called âmodsâ for any Call of Duty game.
Youâre using the wrong tool anyway. Unity is a game engine, which means that it helps you create your own game, not create changes or modifications to existing ones. Iâm sorry if that wasnât the news you wanted to hear, but it just so happens that there is a hidden First Person Shooter template on the Unity website which you can use to make your own shooter game.
Link is here.
To the upper game, i guess you havent played any Call of duty game before. Call of duty is probably one of the most âmoddedâ FPS games out there. You are allowed to do anything from custom code, models, particles name whatever you want, but there is one thing that you are not allowed to do-custom animations. This means that you cant really make custom characters models which i think that it was made to keep in sort of Cod range, becouse who knows that sort of aliens would start to float in this game.
Reallyyy⌠I actually have played Call of Duty games before, many times. I do apologize, I though you meant Modern Warfare 3, but my earlier remark about Unity functions still stands. Unity is a game engine, not a modding tool, and you are using the wrong software. If you want to create your own FPS, then that is where Unity can help you. Many FPS games have been made with it; just search for BeGone or Red Crucible.
The link I gave you earlier will help get you started. Promise.