<div id="wrap">

  <!-- section -->
  <div class="section">
    <div class="center">

      <div id="gallery" class="contains-1">
        <div class="gal"><span>1</span></div>
      </div>
      
      <div id="add">
        <span>Добавить</span>
      </div>

    </div>
  </div>
  <!--/section -->

</div>

html,
body {
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  font-size: 16px;
  line-height: 1.4;
  color: #555;
  background: #fff;
}

* {
  box-sizing: border-box;
}

#wrap {
  position: relative;
}

.section {
  padding: 40px;
}

#gallery {
  margin: auto;
  width: 900px;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  grid-auto-flow: row dense;
  grid-auto-rows: 300px;

  &.contains {
    &-1 {
      .gal {
        grid-row-end: span 2;
      }
    }
    
    &-2 {
      .gal {
        grid-row-end: span 2;
        
        &:nth-child(2) {
          grid-column-start: span 2;
        }
      }
    }
    
    &-3 {
      .gal {
        grid-row-end: unset;
        
        &:nth-child(1) {
          grid-column-end: span 2;
        }
        
        &:nth-child(3) {
          grid-column-end: span 3;
        }
      }
    }
    
    &-4 {
      .gal {
        
        &:nth-child(1) {
          grid-row-end: span 2;
        }
        
        &:nth-child(4) {
          grid-column-start: span 2;
        }
      }
    }
    
    &-5 {
      .gal {
        
        &:nth-child(5) {
          grid-column-end: span 2;
        }
      }
    }
  }
}

.gal {
  max-height: 100%;
  overflow: hidden;
  position: relative;

  span {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 24px;
    font-weight: 700;
  }

  &:nth-child(1) {
    background: #aaa;
  }

  &:nth-child(2) {
    background: #bbb;
  }

  &:nth-child(3) {
    background: #ccc;
  }

  &:nth-child(4) {
    background: #ddd;
  }

  &:nth-child(5) {
    background: #eee;
  }
}

#add {
  width: 100%;
  padding: 10px;
  text-align: center;
  text-transform: uppercase;
  cursor: pointer;
  background: #ccc;
  font-weight: 700;
  margin-top: 20px;
  user-select: none;

  &:hover {
    background: #bbb;
  }

  &.hide {
    display: none;
  }
}

$(function() {
  var $gallery = $('#gallery'),
    i = 1;
  
  function checkGal() {
    var $gals = $gallery.children().length;
    
    $gallery.attr('class', 'contains-' + i);
  }
  
  $('#add').click(function() {
    i++;
    
    if(i >= 5) {
      $('#add').addClass('hide');
    }
    
    $('.gal').last().clone().html('<span>' + i + '</span>').appendTo('#gallery');
    
    checkGal();
  });
});