Step 1: Gather Materials
5 Planks - I usually shoot for five (5) 2x4's cut to somewhere around 4 feet each
2 Front Legs - two (2) 2x4's cut to about 15.5 inches each
2 Back Legs - two (2) 2x4's cut to about 32.5 inches each
2 Supports - two (2) 2x4's cut to about 19 inches
2 back supports - two (2) 2x4 scraps cut to 5 inches each
Screws - it's nice to have a bunch of 2.5 inch screws and some really long deck screws to hold up the back legs
You could use nails.
Paint - I always buy mistint paint. Most paint stores keep paint that they've botched for another client and they try to sell it for cheap. Look for some ultra high gloss outdoor stuff. I try to avoid the solvents and the oil based - personal preferences.
A level - unless you really trust your eyes
A saw - you could do it by hand if you really needed too (also you may try to charm a Home Depot employee to make your cuts)
A drill - with a screw bit for all of these screws or a hammer if you opted for nails
A tape measure - unless you REALLY trust those eyes of yours
All of the benches I built were different, since I was using found materials I needed to change the plan around depending on what I could get my hands on. Obviously those back legs could be lower and you could use the planks from pallets to get yourself a loveseat design that might be a bit lighter. If you follow the above measurements you can build this small loveseat bench using four (4) 8ft 2x4's. With the screws and paint, you should be able to do this for less than $30. If you use recycled lumber it will be even cheaper, and maybe even more interesting!
Step 2: Make All of the Cuts
If for any reason you don't have the means to make diagonal cuts, don't worry about it, I think the design looks great with all straight lines, rigid and square.
I chose to make diagonal cuts on both of the hind legs so that the top supports are at a bit of an angle. Very unscientifically, I made a mark at 1.5 inches at the top of each back leg and then I measured 10 inches down each leg and I made another mark. Then, I drew a line between each mark and cut down the line.
Save the scraps!
Step 3: Build the Front Legs
I build the front legs so that all of the weight from the support and planks will be held up by the 15.5in 2x4's.
So, put the 19in 2x4 flush against the edge of the 15.5in 2x4 and fasten them with some long woodscrews or nails.
You should have two L shapes now, about 17 (15.5+the 2x4 that you just put on top) inches on the short side and 19 inches on the longer side.
Legs and supports!
Step 4: Build the Back Legs
If I know the Instructable community at all, we will see some designs in the comments which are much stronger than this.
I can assure you that some nice long deck screws through the back legs into the supports will hold around 300lbs - but I should emphasize, things have been very unscientific with these benches!
I'm really into symmetry with these things, I like the back legs on the inside. Try it however you like!
Step 5: Fasten the Planks
Since I use such wacky material I sometimes add more screws hoping that things will straighten out. If you use some nice stuff you can probably use just a couple of screws or nails.
I do three planks as the seat spacing the planks with whatever I can find. My mother suggests using a CD case or a couple of CD cases for the spacers, the jewel cases. (What's a CD?)
You could sit on this! (Be careful, it's still really wobbly!)
Step 6: Build the Back
Then after you attach the top bring your spacers back and fasten another support on the back. It's a bit stronger with two planks as the back support and I like the look of it this way.
Step 7: Add the Details
Then on the back, I take each 5 inch 2x4 and I put in 4 or 5 screws to add a bit of support to those back legs. Sometimes I'll cut a 60 degree piece out of these back supports if I'm feeling really designy. It's harder to use these tiny triangles though, I hope you have something in mind.
Step 8: Paint
Now you're ready for paint! I like to buy a nice thick outdoor latex or acrylic from the mistint rack in the best and brightest color they have, then I glob it on in a few coats with the spirit of the amateur.