Rectangular ufo, extremely large, dark red, metal shapes visible, no noise, seen on a clear sunny day.

I have seen a very large rectangular UFO over the lighthouse on Lake Michigan. It was a clear afternoon and I was alone on top of the dunes.  At one half mile away, it was about 200 ft over the lake, no sound, obviously metal, dark red or rust color, about the size of three football fields across by 500 ft high.  There were a lot of circles and angled metal parts that were clearly visible to me. 
I watched it for at least 20 minutes, trying to figure out how a structure so large could just sit in the air.  I turned to go home, turned around for one more look and it was gone.  
I don't remember the date because it was so long ago and I was only 13 years old.
Witness indicates that date is approximate.  PD