btw this is my first Instructable, I'll do my best to explain everything, but if there's something you don't understand or I can do better please leave a comment =)
Step 1: What You Need
sand paper/nail file
paint brush/sponge applicator
Step 2: Draw and Cut
if the bottom(base) is 3' by 3' you would cut 2 of the sides 3' by 2'(height of your choice) and the other 2 side you would cut 2' and 7/8'(3'-1/8') by 2'
of course different cardboards have different thickness, so i suggest that you draw and cut the base first and glue them together(in the next step) and then measure the thickness, then come back to this step and finish cutting the rest of the sides. and don't forget to double the thickness of the cardboard.
I hope that make sense.
okay after you got that down you need to draw and cut 3 of each piece so total there would be total of 15 piece of cardboard.
(if the cardboard is already pretty sturdy and thick, you could just do 2 of each piece, so total of 10 pieces)
Step 3: Glue the Pieces Together
use clips to clip them in place while the glue dry.
repeat this process for all pieces. you will end up with 5 pieces (1 base, 4 sides)
Step 4: Sand and Put the Pieces Together
spread glue on the side of the cardboard and put them all together (I love this part). They should fit, but if they don't you can sand and cut the sides until they do.
hold it for a bit and let the glue dry.
After it dries for a while, you can now sand down the sides even more to make it even more smooth and make the sides flush with each other, but make sure you do this when the glue is absolutely dry.
Now you have a sturdy box! at this point you can just leave it the way it is, but if you want to make it prettyer go on and continue to the optional steps.
Step 5: Optional Steps: Wraping the Box With Paper
(make sure to smooth out the paper after you put on the box, there shouldn't be any bubbles of bumps.)
cut the corners of the paper on the bottom (see image 4) and glue them in place.(image 5)
now for the hard part(which I HATE). cut the loose paper on the top thats not glued anywhere down where the sides are into 4 flaps. Then fold it along the top and trim the sides down until it fits on the inside.(see image 6) Try and cut the corners at an angle (image 7). after it fits inside, go ahead and glue it down. Do the same thing for the other 3 flaps. (it should look like image 8 and 9)
Wait for it to dry.
I know my box isn't perfect. The cardboard is still kind of showing. >.< that's because i trimed the sides a little too much. but thats okay because you can't really tell after you paint it. If you are not going to paint it i suggest that you be a little more careful and make it perfect. =)
At this point you can go ahead and paint it, or just leave it the way it is.
There are many things/ways you can make the box look better, even tho i havn't tried this, but i m sure you can wrap it with fabric, or maybe even vinyle. So use your imagination.
To make the lid, just follow the same steps, but make it a little bigger. Experiment with different demensions, and most of all HAVE FUN!