Material list
1. 1 to 2 cans of glass frosting spray paint. (Most good hardware stores carry a range of colors. We used white.)
2. 6mm or 1/4" masking tape. (Available at car paint suppliers - not a common size available at most paint shops.)
3. General masking tape
4. Scrap paper
5. 6mm or 1/4" sticky-backed lead. (This you will have to get from a leadlight craft store or alternatively you can use a liquid Faux lead available from most good craft or art stores)
6. Scissors and cutting knife for lead
7. Mineral turps
8. Paper towels

A few pics followed by the steps below

Step 1. Make sure you clean the glass window with a mineral cleaner, not glass cleaner.

Step 2. Totally mask off any surrounding areas you don't want the frosting spray to go on to. Cover all furniture with covers. This is common sense really, as you will be spraying inside.

Step 3. Mark out your pattern and then, using the 6mm 1/4" masking tape, place this down on the glass as per your pattern. When the masking tape is removed, these 6mm strips will be where you place your sticky-backed lead.

Any areas you don't want to be sprayed within your design should also be covered with masking tape.

Step 4. Make sure you follow instructions on spray can and then start to cover the window with the opaque frosting. We sprayed over and over the windows, allowing drying time between coats, since we wanted to obscure the view of the shed but this is purely a personal decision and entirely up to you.

Step 5. When the spray frosting is completely dry, then carefully remove the masking tape.

Step 6. Once removed, fill in the revealed lines with sticky-backed lead. We did this by deciding which way would have the least amount of overlapping or cutting and trimming the lead. You could be extremely clever and cut each piece to fit perfectly but if you look at real leadlight windows, the beauty in them is the bumps over the joins.

Step 7. In our design, we have left small areas of clear glass. You could use colored glass paint in these areas if you wish.

The designs we have done are quite formal with a geometric theme but really anything goes. You could check out the stained leadlight section on Google images for other inspirations.

The result was an exciting new dimension to our windows which with care, should last us as long as we wish. Alternatively, if we were to tire of the look, it can all be removed.

Also you could put the lead on the outside of the window, too, so both sides are done, which will give it an even more authentic look. We decided it was unnecessary for ours, since the shed prevents anyone else being able to see the window.