See the scheme to create a plate in Advance Steel using the Dynamo extension.
To define a plate in Dynamo:
In the tree menu on the left, expand the AdvanceSteel tab 
Plates and select ByPolygon. The Plate.ByPolygon node appears in the workspace.
The example below shows how four points are merged into a list of points (the points need to be coplanar). A polygon is generated from the list. Finally, the polygon is used as input for the plate node:
