Blender, Python, create 2d shape from 3d selected faces.

get shape from selected faces.py

import bpy, bmesh, mathutils
    
# Blender script to get selected faces and create a new flat plan from the shapoe
    
    
def createDelaunay(points):
    vs = [mathutils.Vector(co[:2]) for co in points]
    # mathutils.geometry.delaunay_2d_cdt(vert_coords, edges, faces, output_type, epsilon, need_ids=True)
    result = mathutils.geometry.delaunay_2d_cdt(vs, [], [], 0, 0.001)
    vertices, edges, faces = result[:3]
    return vertices, edges, faces

def fnTranslateVectors(arrVerts):
    # Translate the vector into a flattened 2d coordinate 
    avg_normal = mathutils.Vector()
    for v in arrVerts:
        avg_normal += (v.normal / len(arrVerts))
    rot_quat = avg_normal.rotation_difference((0, 0, 1))
    return [(rot_quat @ v.co).to_2d() for v in arrVerts]

def createPolyPlane(vertices,edges,faces):
    # make mesh
    edges = []
    new_mesh = bpy.data.meshes.new('new_mesh')
    new_mesh.from_pydata(vertices, edges, faces)
    new_mesh.update()
    # make object from mesh
    new_object = bpy.data.objects.new('new_object', new_mesh)
    createDelaunay(vertices)
    # make collection
    new_collection = bpy.data.collections.new('new_collection')
    bpy.context.scene.collection.children.link(new_collection)
    # add object to scene collection
    new_collection.objects.link(new_object)
    
# grab currentley selected mesh in edit mode
objMesh = bmesh.from_edit_mesh(bpy.context.edit_object.data)

# get all of the selected verts
arrVerts = []
for objVert in objMesh.verts:
    if objVert.select == True:
        arrVerts.append(objVert)
arrVerts = fnTranslateVectors(arrVerts)
# delaunay_2d_cdt only wants 2d coordinates, and we already have the translated, so just remove Z
vs = [vert.to_2d() for vert in arrVerts]
# pass in verts get back faces
verts_new, edges_new, faces_new = createDelaunay(vs)
# change verts back to 3d in a generic way
arrVerts = [vert.to_3d() for vert in verts_new]
createPolyPlane(arrVerts, edges_new, faces_new)