This is a small cabin boat that sleeps 1 person with lots of space and great to have for kids to play in even in the swimming pool.
The total cost was about $300. The price can vary if you decide to use more expensive materials. (Ex: thicker plywood)

Here are the materials used: (Note: an apostrophe (') denotes "foot" and quotation marks (") denote inches
4' X 8' Plywood Any thickness - 6
2" X 4" X 8' Lumber - 17 (This includes extras in case you mess up)
2" X 4" X 10' Lumber - 2
1 ¼ (1.25)" Exterior Screws - 2lbs
2 ½ (2.5)" Exterior Screws - 2lbs
3" X 6" Mending Plates - 40
2" X 4" Mending Plates - 6
Clear Silicone Caulk - 3 Tubes
Fiber Glass Sheeting and Resin - min. 150 sq. feet

You will also need:
Drill
Drill bits for the screw head you decide
Drill bit (about 1/8")
Caulk Gun
Hammer
Circular Saw
Jig Saw (for angle cuts on bow)

Step 1: Organize and Make Cuts

Create 5, letter-named lumber pieces. (A, B, C, D, and E)
A - 4' B - 3' 5" C - 4' 2 ¼ (2.25)" D - 17 5/8 (17.625)" E - 1' 6" (1.5')
Note: Use the 2" X 4" X 8' lumber for the A, B, and D pieces and the 2" X 4" X 10' for the C and E pieces

You will need 10 A pieces, 11 B pieces, 3 C pieces, 16 D pieces, and 3 E pieces

Measure from the top of all E pieces a 25° angle. 3¾ inches in from the side of the E piece, draw another angle at 70°. These pieces will make p the top part of the bow. Attached is a picture. Erase the lines not shown in the picture and use the jigsaw to cut along the remaining lines.

On all three C pieces, draw a 45° angle from the top. Then on the other end, draw a 20° angle from the top to form a trapezoid. On one C piece, draw a 70° angle from the top 3¾" from the end where you drew the 20° angle. (Refer to picture.) Erase lines not seen in picture and cut with jigsaw along the remaining lines.

Step 2: Begin Assembling the Frame

The main frame is made of 5 basic sub frames. All of the sub frames require the same base. A square. Assemble 5 squares using 2 B pieces and 2 A pieces. Assemble them using mending plates (3" X 6") on both sides of each joint and place them according to the sketch show in the picture for this step (Note: Do not use mending plates on both sides of the front square sub frame). Designate the rear frame, the middle three, and the front frame. Place a third B piece between the existing two B pieces in the same fashion on the rear frame. On the front frame, screw the C pieces in where shown in the previous step using the 2½" screws after using the smaller mending plates to attach the C pieces to the E pieces as shown in the picture. Once finished with the top, screw in, using a combination of small and large screws, the bottom part to the front square pieces. Then assemble the front square using large mending plates.

Step 3: Complete the Frame

Attach the D pieces on the top and bottom of each square starting with the back square. Place the D pieces 1' in from each side and fasten using the large screws. On the next frame, place the D pieces 1'4" in from the side and attach in the same fashion. Continuing Alternating placement until you get to the front. (Refer to Picture.) After this step, the frame should be complete.

Step 4: Begin to Assemble Exterior

First, cut and label the plywood in the same fashion you did the lumber, except using the numbers. Here are the dimensions:
1 - Leave 4' X 8' (1)
2 - Cut at an angle so the top is 8' and the bottom is 6½'. (Do this by measuring lengthwise on both sides and drawing a line between the two marks. (2)
3 - Cut 1½' off of one end to make the whole 6½' X 4' (1)
4 - Cut 3' 2¼" off of one end (1)
5 - Cut 4' off of one end (Cut directly in half) (1)
Piece 1 is the top, 2's are the sides, 3 is the bottom, 4 is the front, and 5 is the back.

Step 5: Assemble the Exterior

FIRST. Any door you would like made must be cut before application of the top. NOTE: Cut door large enough to hit the lumber frame when closed so that people can walk on it. Make sure there is a lip underneath the door.

Place the No.1 piece on the top and screw it into all parts of the frame. Then place the sides on the boat and attach in the same fashion. Once finished with the sides, move to the back. Once finished with the back, flip the boat on its side ad attach the bottom and front.

follow the instructions for use on the fiberglass and apply to the bottom and sides. The top is optional, but if you want to have anything wet (like swimsuits) on the top, I recommend using the fiberglass on the top as well. be sure to cover all edges with the fiberglass thoroughly.

Use the extra plywood to put a floor over the lumber frame on the inside and you have completed your mini cabin boat!