Install any internal walls and shelving. I've used 18mm ply for this. It's not a structural grade so I've been careful to paint it and keep the bottoms from touching the ground.
Step 2
Install brackets for bike, boats etc. Plenty of hooks are another handy addition. Use screws to do this as things can change and you will want to move with the times.
Step 3
Build the doors. First measure the cavity and work out the door size. They don't have to be the same width it may be advantageous to have one smaller than the other so keep an open mind. I've constructed a rectangle with a brace running through it then covered it with 4mm marine ply. I've used 12mm ply to strengthen the corners.
Step 4
Hang the door and paint it.
Step 5
Hang the tarp. Bunnings has tarps in heaps of different sizes but it's the width that's the most important: it needs to be as close as possible to the size of the opening, if anything slightly bigger. Attach two lengths of pre-painted timber (I've used 12mm ply) across the bottom of the tarp, front and back, sandwiching the tarp in between.
Step 6
Drill a hole at each end of the timber to allow for tying. Hang the tarp using a baton to attach it to the roof. Fix small hooks to the frame of the storage unit to attach the tarp.