Homemade Wood Putty
For a natural wood finish putty. Instead of store bought putty.  After cutting your material.  Save the fine sawdust..
Make a putty by mixing the sawdust and Elmer’s white glue (not yellow carpenters glue).  Apply the putty to nail holes.
The putty will then match the woods own color.  Use sparingly to minimize sanding.

Plywood
Plywood was invented and used in the mid 1800's.  The first (machine made) mass production of plywood was in 1907.

Door Sizes
2-0 door = 24", a 2-4 door = 28", a 2-6 door = 30", a 2-8 door = 32", a 3-0 door = 36"
Typical door height is 6-8 = 80".  Example:   2-6 / 6-8 door would be a 30" x 80" door.
The chart below shows the typical rough opening size required for the door and door jamb (frame).
Door Size               Rough Opening Size
2' 0" x 6'8"  (24" door)             26" x 82 3/4"
2' 2" x 6'8"  (26" door)             28" x 82 3/4"
2' 4" x 6'8"  (28" door)             30" x 82 3/4"
2' 6" x 6'8"  (30" door)             32" x 82 3/4"
2' 8" x 6'8"  (32" door)             34" x 82 3/4"
2' 10"x 6'8" (34" door)             36" x 82 3/4"
3' 0" x 6'8"  (36" door)             38" x 82 3/4"

Figuring Sq. Ft. and Sq. In.
Feet x Feet = Square Feet
Inches x Inches = Square Inches
Total Square Feet times 144 = Total Square Inches
Total Square Inches divided by 144 = Total Square Feet