Bricks are a type of peg which can be straight or curved and are typically rectangles with a width of 20. They should have PegInfo which holds the peg properties such as Can Be Orange. See Pegs for more information.
Technically curved bricks are polygons in the shape of an arc. However they are small enough to look like they are round. However if they are larger and straight lines show on the brick, you can increase the number of vertices so that it appears more rounded.
Curved bricks are defined by sectors of a circle. When hovering over bricks in PeggleEdit, the inner and outer ring will be displayed showing how the brick fits as a sector in a circle. There are two properties to define the brick.
Length / Radius defines mostly the brick size.
Sector angle defines how curved the brick is.