You can't even make a design using standard off-the-shelf chips;

You can't even formulate a broad requirement specification for your project - how are you going to come up with the detailed specifications that will be required to design & manufacture a custom chip?!

Making a custom chip is not a case of just trying stuff, and then trying again if it doesn't work; making a custom chip requires it to be right first time...

You can't just cut tracks and put strap wires onto a custom chip!