CTF maps are very simple to make. We only need a few entities and a couple of trigger brushes to have a working CTF map for TF2.

Place the Intel

We are going to create the intel for the blu team first. Using the entity tool select item_teamflag.

Now, place it where you want the blu team’s intel to me in the map. Open the object properties window for the teamflag (double click it, or press alt+enter with it selected), and give it a name; blu_intel will be good enough. Select CTF for game type, and Blue for the team. If you want you can set the return time lower (or higher), but I am going to leave it at 60 seconds.

Set cap zone

Create a brush surrounding the area you want to be the cap zone or the area where players have to enter with the enemy intel to capture it. This brush will be a trigger of sorts, so use the trigger texture. With the brush selected, press Ctrl+T and select fun_capturezone. Again, we need to set a few options here.
Give it a name, blu_cap is what I went with, and select Blue for the team.

Repeat

All that is left to do is the same thing for the red team. Just change what was blue to red, and your map is ready to be compiled!

I have included my example map here on our forums. Feel free to ask any questions!