To mark the centerline, set a compass to span something more than half the width of the leg. Draw an arc from corner of the leg. The point where the arcs intersect will be on the centerline. With a centerline point on each end of the leg, place a scribe on the point, slide a straightedge up to touch the scribe. Do the same on the other end. When you have the straightedge positioned so that you can touch both points with the scribe, and in each case it is touching the straightedge - without moving the straightedge - scribe the line. Use scribes, rather than pencils or pens, because they make more precise marks.
The next day, cut it flush. Use a block plane to ensure it truly is flush. This will be the top of the bottom layer of the bench top, so gouges aren't a problem. (Wiping up glue with a damp cloth can lead to stains and finishes applying unevenly. That won't be a problem here, either.) But bulges and bumps are a problem - they will keep the two layers of the top from matching up evenly.
In the Port Townsend School of Woodworking’s twelve-week Woodworking Foundation course, you will learn the essential skills, tools and mindsets of the traditional joiner. This is NOT an industrial arts course with a focus on machinery and production processes. Rather, it is a course in PRE-industrial artisanship--the creation of individual works through mostly hand tools and skills.. 
I recently came across this beautiful wooden swing set, which was made in the shape of a boat. Cool, isn’t it? The very first look was enough for me to start loving it. Although I haven’t yet tried building one myself, I am definitely going to. Later I realized that you can also build a baby cradle with the same idea. After all, what can be more calming than the tender rocking of a boat? This swing set will surely help your child get more gentle sleep.

The source above is not exactly a tutorial, but it gives you a basic idea of how the author built a Quirky Pallet Art to enhance the look of their old house. You can also find another tutorial at the link below. It shares a step by step procedure for making a wooden pallet sign. The final product is not exactly the same as the one above, but the basic idea is the same.
The oldest woodworking shop in America has been discovered virtually untouched in Duxbury, Massachusetts. The extremely rare find reveals an 18th century joiner’s shop with the date ‘1789’ painted in the rafters. University of Delaware professor Ritchie Garrison came upon the historic structure on the site of a preschool, bringing several experts out to verify its age. Craftsmen used the shed to create intricate woodwork.
Olympia Tools is a bit of a lesser known manufacturer. While they offer a wide range of products for a variety of construction fields, they are definitely more of a budget option. That said, Olympia Tools is one of the few brands that manages to produce a reasonable quality at a low price which makes them a solid choice for customers looking to get the best bang for the fewest bucks.
The shelf in the first picture is made of red oak plywood. You can choose the wood type, color and design as you like for your project. In case if you need more help understanding this project, you can refer the source link below. It discusses various items used, steps and tips and personal experience of the author who personally built a Zigzag shelf.
I agree that even at 12x12, things'll be "cozy" inside. That's OK. Keep in mind that this will be a general purpose hobby shed, not just a wood working shed. Even 12x8 would be plenty big enough for building 1 meter wingspan bungee launched RC gliders. And for the electronics projects I do, I only need enough workbench space to do some soldering with a 3rd hand (for electric guitar pedals). If I need more room than the shed offers for wood working projects, I'll just roll the table saw down a ramp and do my cutting outside in the sun.

We have more than sixty years of excellence (1956-present) with an annual enrollment of more than 1,000 students in over 35 different classes.  The Palomar College Cabinet and Furniture Technology program offers the most comprehensive woodworking career curriculum in the nation. Utilizing three fully-equipped shops, our 2 full-time and 20 part-time instructors provide a breadth of courses and depth of expertise impossible to obtain in smaller programs.
Stop it. Really. I mean it. Pick a height between your thigh and waist that seems right. You’ll adapt. Don’t worry about your back. You’ll adapt. If you are really uncertain, make it a little taller and then cut down the legs. After a decade or so, your work habits will put a magic number in your head. You’ll have built enough furniture that you will know your number. Until then, pick a number.
I agree that I might quickly outgrow a 12x8 shed. Lowes also offers a 12x10 Rancher (same style, but more room), but the 12x10 is 9 feet, 4 inches high, and my community only allows a maximum height of 9 feet. The 12x8 is exactly 9 feet high. I'm afraid of getting "out of spec" if I exceed the height limit and then getting in trouble with the Home Owner's Association. Having said that, 12x10 would be about the biggest size I could get for the available area in my back yard, so even if I hire a shed contractor to do this, the shed would have to be 12x10 or smaller.