One of the main kinds of multiplayer custom maps are tower defenses. In this kind of game there are four main components.
Your builder
This is the unit you tell to build towers for you. He is usually what your main focus will be on for the game. The Builder is very important.
Building area
This is where you are aloud to build your towers. It should be near or directly under where you spawn your builder or where your camera is first located when the game starts. This should be the only area where you build towers unless someone asks for a specific tower built in their area. It is generally rude and disrespectful in other cases to build in other players building area.
The Enemies
These are what you will be killing in most cases they are just normal creeps and they come in waves each wave with more hit points and armor and different types of armor. Although some waves may have special effects. For example there are some Tower Defenses that have “immune” waves that are immune to slowing effects and magic attacks from towers.
The enemies' goal
This is what you are defending, You do not want any creeps/monsters to get to this object. In most tower defense games if a creep gets to this goal you and your team will lose a “life” although in some tower defenses the enemies goal will have hit points and you will have to keep the creeps from getting their goal to 0 hit points.
The easiest way to prevent the creeps from reaching their goal would be to “maze” mazing is building your towers in a fashion that it would take the creeps much longer to get to their goal. The most common type of mazing is to weave line s of towers back and forth with 1 space in between the lines.
Have fun with playing Tower Defenses!