From Unreal Wiki, The Unreal Engine Documentation Site
This creates a cylinder for the red builder brush.
- float Height
- the height of the cylinder
- float OuterRadius
- The radius of the cylinder.
- float InnerRadius
- applies only when Hollow. The radius of the hollow part
- int Sides
- The number of points at the sides. The more points, the rounder it looks, but when too many, the game gets slower.
- name GroupName
- doesn't work with it
- bool Align to Side
- Aligns the textures to the side
- bool Hollow
- makes ik hollow
- BuildCylinder( int Direction, bool AlignToSide, int Sides, float Height, float Radius )
- bool Build()
 Alignment tips
I don't really know how to align cylinders properly. Just do align wall direction and panning, and then it looks ok enough.