Attach the snow rake to a long extension pole. Snow rake kits usually come with long extension poles to reach high areas of the roof.
Face the cutting wire on a commercially available roof rake toward the roof. Place the roof rake at the edge of the roof just above the gutter.
Push the roof rake's wire toward the peak of the house as far up the roof as possible. The wire undercuts the snow as you push the rake forward.
Turn the rake over at the same point at which you stopped the forward motion. Pull the rake through the snow and drag the snow off the roof. Leave a 1- to 3-inch snow base on the slate roof.
Move to the left or right and push the wire side of the rake up the slate roof, turn the rake over and pull the flat side down the roof to remove the snow. Continue to move the rake over and clear snow from the roof until no snow remains. Move to the other side of the house and repeat the process.