Simple Polygon

HTML

<div id="map"></div>
 <!-- Replace the value of the key parameter with your own API key. -->
<script async defer
src="https://maps.googleapis.com/maps/api/js?key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk&callback=initMap">
</script>

CSS

#map {
  height: 100%;
}

html, body {
  height: 100%;
  margin: 0;
  padding: 0;
}

JavaScript

function initMap() {
  var map = new google.maps.Map(document.getElementById('map'), {
    zoom: 5,
    center: {lat: 24.886, lng: -70.268},
    mapTypeId: 'terrain'
  });

  //Coordenadas
  var polygonCoords = [
    {lat: 25.774, lng: -80.190},
    {lat: 18.466, lng: -66.118},
    {lat: 32.321, lng: -64.757},
    {lat: 25.774, lng: -80.190}
  ];

  // Construct the polygon.
  var polygon = new google.maps.Polygon({
    paths: polygonCoords,
    strokeColor: '#FF0000',
    strokeOpacity: 0.8,
    strokeWeight: 2,
    fillColor: '#FF0000',
    fillOpacity: 0.35
  });
  
  
  polygon.addListener('mouseover', function() {
    polygon.setOptions({fillColor: 'green'});
  })
  
  
  polygon.addListener('mouseout', function() {
    polygon.setOptions({fillColor: '#ffffff'});
  })
  
  
  polygon.setMap(map);
}