James... It isn't so easy. For creating your own map u can spend many months.
And try to check forum on the official ZPS site: zombiepanic.org
There u can find lot of staff linked with mapping.
So u will see at least. What it is.
And plz. Don't take it bad. I don't wanna make leave you in a bad light or something else...
Simple check it 1st. One time i wanted to make my own map too. I downloaded tools for it, set up it. But on it almost all ended xD.