I had to make a new door for the garage workshop as the existing door was rotten and hanging off of one hinge. I decided to re-purpose the door as a work bench table for someone else.

Working with an old door such as this, I would recommend wearing a face mask to protect from dust/dirt and old paint.

The tools you need are basic, I used the following:
Hand Saw
Hammer
Set Square
Sharp Wood Knife
Power Drill (or Hand Drill)
Mitre Clamps & Other Clamps
Shifter
Pliers
Pencil

Materials:
Old Door
Scrap Pallet Wood Plank
90 x 35mm Pine for Table Legs / Stand
42 x 19mm Pine for Cross Bracing
Bolt
Wing Nut
Angle Brackets
Screws

I have made a video as well as put some text and pictures.

Step 1: Remove Rotten Wood

On the door, there was some rotten pieces that I needed to attend to to strengthen the door.
The horizontal brace at the bottom of the door had to be completely removed.

I then brushed off the dust on the door where the brace was, measured up a new piece using a pioece of scrap pallet wood.

Step 2: Cut New Horizontal Brace

After measureing the size I needed for the new brace, I held the wood inplace with a clamp, scored the wood with a knife and set square, then used the hand saw to cut it to length.

Step 3: Attaching New Bracing

Now the piece is cut, I measured an equal distance from the middle brace downwards, then I applied PVA glue (this is why cleaning the wood is important so there is no dust), then moved the piece into position then used screws to fix it in place.

I also added additional screws to the other bracing to strengthen the door and make it more rigid.

Step 4: Remove Door Hardware / Remove Loose Nails

Now the door is more solid, I removed all the door hardware - Door knob, sliding bolt, lock etc.

I also removed loose nails, or I hammered them back into the door.

Step 5: Make Stands / Legs

I used the 90 x 35mm timber to make rectangles. These will be the main supports for the door/work bench.

Cut the wood to size to suit the height you want, mine is about 850mm high, then glue the ends, clamp then screw the pieces together.

Step 6: Cross Bracing

I used the 42 x 19mm timber to make diagonal cross bracing to hold the stands in place.

The cross bracing was screwed to each stand, then a piece of wood was placed between where the cross bracing meets, then I drilled through the bracing and block of wood so I could insert the bolt and wing nut.