I'm not sure you're understanding that TF2 and Garry's Mod are very different games that require very different map designs. Now I won't stop you from building this map how you want, but just hear me out:
"Testing a map in TF2" doesn't just mean loading the map in TF2 and seeing if it works; it's also about testing for good gameplay. All official TF2 maps are designed specifically for the way TF2 plays, and include places for each of the nine classes to be useful. They also follow general design standards for each gamemode and are scaled properly to account for the fact that most combat in TF2 is resolved at close range. On the other hand, many Garry's Mod maps are made for roleplay and often have large open areas, which are frowned upon in TF2 for class balance and performance reasons. In order to better understand this difference, I would recommend playing TF2 more and paying attention to the map layouts and class roles, seeing as you only have about 9 hours logged in the game.
Also, this community primarily tests maps that are designed and built for TF2 from the ground up. As such, the feedback you get from our testing events is probably not going to be what you want to hear. You will most likely get comments suggesting that you make drastic changes to the map to make it more suitable for TF2 gameplay. If that's what you want, great, take the feedback in stride and study other CTF maps to improve yours. If not, then our testing events may not be for you. Just a heads up.
Again, I'm not going to tell you how you should design your map, but I wanted to let you know what kind of community this is and what you should expect by bringing such an unconventional map here. We're not like GameBanana where anything goes; our focus is more on developing high-quality maps that fit the TF2 style and could potentially be accepted into the game someday.