A shed is a great project to earn your sawdust legs on. It is just some very basic carpentry skills. You could build the whole thing with a circular saw, hammer, utility knife, pencil, and tape rule. Find a friend or relative that has some decent skills to help. You could do it in a weekend. Keep the size on a four foot increment to minimize wastee. I would recommend a 12 x 12 or a 12 x 16 if you can. If you don't want to cut any rafters (which is really a simple process), you can order small triangle shaped trusses for the roof from your local lumberyard. If you are using T1-11 for the sides, get the real plywood based stuff, no waferboard. Same thing for the floor, use plywood (treated if you like). Cedar for the trim, not pine. The visqueen underneath is a good idea. Insulate the walls inside to help temper temperature swings. Build overhanges into the roof all the way around, 12" is nice. These really are a fun project. You can add a small window with a flower box underneath to make it look a little homey too.
I made a low table out of a couple of step-stools, my hollow-core door, and one of the MDF panels that would eventually form part of my top. I was concerned that any oil that dripped on the door might interfere with its glue adhesion, when I finally get around to the project for which I'd purchased it. The top side of the top sheet of MDF, though, I planned to oil, anyway. (Ditto for the bottom side of the bottom sheet.
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.
When the holes were complete, I flipped the legs and drilled the countersinks with a 1" Forstner bit. Trying to drill a countersink when the center was already drilled would be impossible with a spade bit or an auger, but Forstner bits are guided by their edges, not their center, so they can handle this job. On thing about Forstners, though -- they have a tendency to skitter around a bit when starting, before they bite. An easy fix for this is to drill a hole through a piece of ply, and to clamp that to your work, creating a jig that will prevent the bit from drilling in the wrong spot.
My bench is MY BENCH. In other words, it’s a thing of evolutionary beauty. I built the top 10 years before deciding on and designing the base. I spared no absurdity. It is supremely stout and the much maligned drawers are accessible from either side. The larger drawers have dust lids and can be extended to provide support for large workpieces or as a step for climbing on top of the bench. The top alone weighs more than most Roubos. So NYAH! Did I mention that I designed it to fit in with the Arts & Crafts vernacular? Who said you can’t build your bench to be furniture? Beautiful as well as useful shop furniture? Just sayin…
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Out of all the shed books I have read, this book stays by my side while I hammer in the yard. The book is well written by what appears to be a non professional book writer (A Good Thing). It reads as if you are getting advise in laymans terms from your neighbor "The Craftsman", a welcome change from the DIY books, that assume a level of expertese. The level of detail is high and discusses gotcha's, advise, and trade "secrets" that could have only come from years of personal experience building sheds.