Made this for a friend who likes to go out into the world to paint; but it'd be just as handy for keeping organized at home.
Oak, .25 x 36 x 36"
(3) Oak, .5 x 2 x 36"
(2) square dowel, 3/8 x 36"
1/2 yard of cloth
1 spool of leather stripping
hinges (I used 3, 2 large, decorative hinges, 1 small "middle hinge")
Obviously you can substitute whatever kind of wood you want to use; I got all of mine at Lowes for about $20. For the cloth, check the remnants bin at Walmart or whatever fabric stores you have nearby, you need 2 pieces that are just shy of 12x16", so you don't even need half a yard, really, and you can get remnants cheap.
Step 1: Construct!
Cut your 2x2' piece into 2 12x16" pieces; this is your top and bottom.
Split the 2x36" pieces into 4 15.75" and 4 11.75" long pieces; these are your sides. Save the rest of the 2" wide wood for later.
Glue 2 of each length side onto the bottom of each top/bottom piece, overlapping the corners. (I should've taken a picture of this, as it's hard to explain using words. Each side piece should have an end butted up against 1 piece, and the other end clear.) Carefully flip it over so the sides are supporting it, and using small nails, nail the top to the sides: 1 nail at the corner, and 1 about 1" from the center nail on either side.
Once the glue is dry, drill your screw holes for the hinges and clasps.
Step 2: Stain
If you're going to stain the box, do so now. I wanted to leave the interior of mine natural, but if you want to stain that, you'll need to cut your interior dividers now, check the fit--do not permanently place them yet!--and stain them separately. I used masking tape to mask the bottom ledge of each box half & keep it the natural color.
Step 3: Interior!
Trim your cloth so you have 2 pieces the exact size of the floor of each box half.
Decide on your tie-down placements, cut the leather strips to length, and hot glue those in place.
Cut a hole for each strap in your cloth, then thread the strips through and hot glue the material down.
If you want to add any exterior decoration (I added an ink-drawing of a paintbrush to this one), do so now.
Step 4: Interior, Part 2!
Cut your interior dividers to length and glue them in place. I went with the 3/8" dowel for most of the box, for smaller items: pastels, tubes of paint, pencil sharpeners, erasers, whatever. Then the 2" for bigger items and brushes, pencils, and whatnot.
This will work out better if you use some scrap wood--the leftovers from your 2" and 2x2' pieces will work perfectly--and something heavy to press the dividers down. There are almost certainly parts of your lining that aren't directly glued down, and you don't want your divider flopping around because of it.
Step 5: Final Assembly!
Once everything's dry, time to put it all together. This will go smoother if you use clamps to keep the box halves lined up while you're screwing in the hinges and clasps.
Once that's done, that's that! Go put some stuff in your new box.