I just got through building one. Found the idea on Archery Talk.
It's a 4' x 4' double sided target built out of 2x12's and some 1x4 trim. I got the target facing from a place called Third Hand Archery. It was $30 for the pair of target skins. It's packed pull of old clothes and stops a 300 fps arrow point blank about 6" deep. And you can pull it out with two fingers.
Here's a copy and paste of the plans. I added wheels to mine so I could move it around.
materials list
1 board 2"x12"x8'. Cut into one board 48" and one board 45"
1 board 2"x12"x12'. Cut into two boards 6 foot.
1 board 2"x8"x8'. Cut into two boards 2"x8"x3'. To be used as the feet to hold the target upright.
4 boards 1/4"x1 1/2" by 8'. Cut 4 boards 45" and 4 boards 48" for trim.
2 sheets of black plastic film 4'x4'
Staples and 3" wood screws.
A bunch of old clothes. About 3-4 55 gallon bags
1] cut a 8"x36" trap door in the middle of the 48" 2"x12"
2] lay boards on floor and screw the 48" 2x12 into the top of the two 6' 2x12's. Use a square when screwing them together.
3] Measure from the top of the top board down 48" on both 6' 2x12's. Keep the <font color="#FF0000">bottom of the 45" board on the 48"mark. Screw the 45" between the two 6' boards.
4] Staple black sheeting to front and back of box on all four corners. Over the top of the black plastic sheeting, staple all 4 corners of the skins snug without sagging. Once all four corners are snug then staple every 2" all the way around.
5] Screw in the trim boards overlapping the joints of the 2x12's.
6] Stand up target and screw in the 3' boards at the bottom of the 6' legs to make a foot to assist holding the target upright.
7]Toss the clothing in, cramming in the corners first and fill to the middle. For the higher poundage bows cram the rags in tighter all the way to the top.
