I've now made three pallet benches, a cheap and easy to make alternative to expensive garden furniture.

The exact design of your bench is going to rely on the pallets you can get your hands on and what state they are in.

Adapt your design to match what you can lay your hands on.

Step 1: Tool List

Here are my essential tools:

Something like a crow bar, or in my case a strong old screwdriver
A claw hammer
A box of exterior screws. I used some left over deck screws.
An electric screw driver. You could use a hand screw driver but this is nice and quick.
A Jigsaw (My go to tool for almost every build :-) )
A tape measure or long ruler
A set square

Step 2: Select Your Pallets

Select your pallets. I managed to get a couple of sturdy ones from a building site locally.

They are both pretty heavy and should stand up to being outside for a few years.

Step 3: Cut the Seat

The essential elements of a bench are that, when sitting on it, your feet reach the floor without your legs being bent up or the edge of the bench putting pressure on the back of your thigh and the rear of the bench not digging into your back.
From my experience, the best measurements are:

The seat of the bench should be 40 cm off the ground
The seat of the bench should stretch back 40 cm
The back of the seat should be at least 35 cm high
The back of the seat should slope back 1 cm for each 20 cm it is high

As you can see in the first photo above, I have cut the pallet into three.

The left hand part will be the front of the bench.

The right hand part will be the seat.

Therefore the right hand piece has been cut at 40 cm from the right hand edge and the left hand piece has been cut at 23 cm, 40 cm minus the depth of the pallet, which in this case was 17 cm

In the second photo above, you can see the front and the seat placed together.

The centre section wont be wasted. That is going to be used for the sides.

Step 4: Prepare the Back

Take the top of a second pallet to use as the back.

Remove it from the pallet base using the claw hammer and crow bar.

Remove the nails from the back of the pallet. You could use a hack saw, bang them out with a hammer or in my case get my son to cut them off using an angle grinder and suitable safety attire while creating showers of sparks.

Step 5: Add the Sides

Add sides to the bench. These are made from the centre of the first pallet that is cut in half.

In the design I am making, I'm going to add arm rests, but you can make the sides lower if you don't want them.

Attach the front and seat of the chair to the sides using screws.

Cut the side of the bench that will attach to the back so that the back will slope 1 cm for each 20 cm it is high.

I did this after attaching the sides as I think it is easier to get the measurements right. You could cut it before attaching if you think it would be easier.

Step 6: Attach the Back

Attach the back of your bench to the front and sides.

I can't really tell you how to do this as all the pallet benches I have built seem to have different elements that are strong enough to hold the screws firmly. The basic idea is to make a strong join between all of the parts, making sure none of the screws are sticking out.

In the photo, you will see I left part of the pallet in place on the sides to support the arm rests. This turned out not to match the width of the arm rest wood I had, so I removed them. This seems to be the main essence of making things from pallets. Adapt your design to match what you have.