Making a Zone of Fire for RTS

Hi.
I am trying to designate a Zone of Fire function for an RTS.
I want the player to be able to designate either a forward area or a circle around the unit as the zone.

In the case of a wedge like zone, the player clicks the unit, chooses ZoF and then chooses either wedge or circle. If the wedge is chosen, the wedges tip is placed at the unit and the player clicks on the map to place the two points of the base of the wedge.
If circle is chosen, the player clicks to decide the circles radius.

(Any pawn/actor that moves within the ZoF (and is within the units line of sigth) is a valid target.)

What I would like help with is the best way to set up this fuction. I have tried using a procedural mesh, but I could not figure out how to turn a plane into a volume and was worried that it might be expensive.

What I need is a trigger area (or similar) that:

  • allows the player to set the radius/size in runtime.
  • is visible as a 2d texture (projected on top of the terrain).
  • extends to the z axis, able to detect actors above/bellow the unit.
  • follows the unit around but retains its direction.
  • discovers when any unit (friend or foe) is wholly or partially within it.

Example from Combat Mission: