AUBuilding.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using MonoTouch.CoreLocation;
using MonoTouch.MapKit;
using System.Xml.Linq;

namespace Auburn.Models
{
  public class AUBuilding : MKPolygon
	{

		public static AUBuilding FromData(Building b)
		{
			// this cast doesn't work.  it was worth a shot.  :)
			var points = AUBuilding.BuildingPoints(b.kml);
			var poly = AUBuilding.FromPoints(points) as AUBuilding;
			poly.building = b;
			return poly;
		}

		/*
		 * Either this should work, or I should be able to set some unique identifier on a plain MKPolygon object.
		 * 
		public override MKMapPoint[] Points {
			get {
				return new MKMapPoint[10];
			}
		}
		*/

		public Building building { get; set; }

		public AUBuilding (Building building)
		{
			this.building = building;
		}

		public override string Title { get { return building.name; } }

		public static MKMapPoint[] BuildingPoints(string kml)
		{
			var list = new List<MKMapPoint>();
			
			XElement xe = XElement.Parse(kml);
			IEnumerable<XElement> coords = xe.Elements().Elements().Elements();
			foreach (var coordXML in coords)
			{
				var coordString = coordXML.Value;
				foreach (string coord in coordString.Split(" ".ToCharArray()))
				{
					var coordEntities = coord.Split(",".ToCharArray());
					list.Add(MKMapPoint.FromCoordinate(new CLLocationCoordinate2D(double.Parse(coordEntities[1]), double.Parse(coordEntities[0]))));
				}
			}
			return list.ToArray();
		}
	}
}

MapViewController.cs

var kml = @"<Polygon><outerBoundaryIs><LinearRing><coordinates>-85.4867142869,32.6004323223,0 -85.4867434496,32.6004763692,0 -85.4867107582,32.6004907865,0 -85.4867714882,32.6005893807,0 -85.4864231987,32.6007430277,0 -85.4864764096,32.6008294527,0 -85.4864111298,32.6008582695,0 -85.48635866,32.6007730838,0 -85.4862478436,32.600821977,0 -85.4860059567,32.6004291414,0 -85.4865266665,32.6001993966,0 -85.4866795242,32.6004476574,0 -85.4867142869,32.6004323223,0</coordinates></LinearRing></outerBoundaryIs></Polygon>";

var bdata = new Building()
{
	name = "Parker Hall test",
	kml = kml,
	id = 7
};

// this cast doesn't work.
//var building = (AUBuilding)MKPolygon.FromPoints(AUBuilding.BuildingPoints(bdata.kml));

// this doesn't work for the same reason.  i can't cast from MKPolygon to AUPolygon
//var building = AUBuilding.FromData(bdata);

// this does work, but I can't figure out how to set a unique ID or add a custom field
var building = MKPolygon.FromPoints(AUBuilding.BuildingPoints(bdata.kml));

mapView.AddOverlay(building);



mapView.GetViewForOverlay = (m, o) => {
	if (buildingView == null)
	{
		// How do I get a unique ID for my current MKPolygon?
		buildingView = new MKPolygonView(o as MKPolygon);
		buildingView.FillColor = Constants.PrimaryOrange;
		buildingView.Alpha = 0.5f;
		buildingView.Tag = 7;
	}
	return buildingView;
};