It is beneficial for you and your marine animals to have a wooden hood covering the fish tank. Not only does the enclosure provide more security, it also keeps objects, dirt and dust from collecting on the water. It can even hold a light, if you wish.
Measure the width and length of the top of the fish tank. Add a half-inch to each measurement so the lid will rest over the top.
Put on gloves and trim your wooden boards, two for the width, two for the length.
Set one of the longer boards and one of the shorter boards on their edges. Place the shorter board perpendicular to the side of the longer board, making sure the edges are even. This should create an "L" shape. Fasten the board edges together with nails or screws. Fasten the other smaller board to the other end of the longer board. Your hood should resemble a box with one side missing.
Lay the second longer board flat over the top of the smaller boards, opposite the first longer board. Line up the edges, then fasten it with nails or screws. This board is secured differently because it will be the back of the hood and must allow space for your aquarium's cords. It also provides additional support to the frame.
Use the wooden cubes as anchors on the inside of the hood to keep it from slipping. Fasten the cubes to the middle of the inside of each board, about 1 to 1-1/2 inches from the bottom edge of the board. Set the hood over the tank to make sure the cubes hold it. If they do not, add more cubes.
Trim the plywood to the measurements of the top of the tank (plus 1/2-inch). Space the hinges evenly apart and screw them into one side of the plywood.
Place the lid on the hood, lining up the edges to make sure the hinges line up with the back wooden board where the cords will exit. Screw the hinges' sides into the back board of the hood to create a lid that opens easily. Place the hood on top of the fish tank, and make sure it fits well.
You can paint or varnish the hood and add decorations if you like.