I tried your map for a few minutes. I found all the items (dynamite, key...) but then I was stuck. A redbox appears on the bottom of the wall, it doesnt trigger anything.
It's not bad for a first attempt with hammer! Try to focus on quality rather than quantityor size, and always think about balance (zombies don't like large open areas). Try to bring some variations (the players only have to break doors and walls at the beginning) and be sure to not frustrate the players (confusing paths, ladders trying to kill you...).