Measure twice and cut once.

Know the mirror size focal length and design the telescope around that.

The primary mirror mount attaches to the baseboard with 3 adjustable screws. The screws have to push and pull on the mount and thread against the baseboard, so consider various fasteners like friction nuts or pronged tee nuts, and maybe wood glue or epoxy.

With the mirror mount on the base, you can attach the fenceposts to the base and framing to the top of the fenceposts, around about where the spider mount will go. 

Use a street lamp or a full moon to find the focal point relative to the body of the telescope and thus determine where the spider mount and lens should go. I carved a rough hole in a small piece of plywood for the lens; used bike spokes for the spider mount and drilled holes in the fence posts to mount the spider mount on the fence posts.

As in the YouTube video of Dobson building his telescope, find the center of gravity for the telescope and build the mount using sections of fenceposts. I wrapped Teflon tape around where the altitude mount pivots in a see-saw motion to make the telescope pivot smoother around the altitude mount. For an altitude motor drive, use the 3D printer screw and a stepper motor. The stepper motor mounts to the stand and the screw pushes and pulls against the body of the telescope (see project images). Make use of the 3D printer bearings that commonly come packaged with the 3D printer screw to have smoother rotating parts.

The azimuth mount can swivel by rotating one layer of the telescope stand sandwiched against another layer of the telescope stand. Use a Teflon gasket and vinyl record like bearings sandwiched between the two layers, as in Dobson's YouTube video. I used a long bolt (such as a toggle bolt) as a spindle. For a motor drive, fix a bike chainring against the underside of the upper layer of the telescope base and fix the stepper motor to the outside edge of the lower layer of the telescope base (see project images). Use shims (I used pieces of the 1sqin fencepost) to elevate the base of the telescope off the ground so that the stepper motor is aligned with the chainring. Use a small cog/sprocket and large chainring to get a good gear ratio for a modest stepper motor to torque the telescope for a functioning drive. I found creative ways to attach the sprocket to the stepper motor, to make the azimuth spindle just tight enough to minimize vibration and just loose enough to allow the stepper motor to move the telescope. Get creative with the mount and the vinyl/teflon bearings. I used a plastic strip from a plastic bottle to keep the bike chain aligned on the gears.