I've been doing these "trays" for a long time now, mostly on hollydays, at the beach house when you got time to spare and there's nothing to put your ashes in.
Be really carefull while doing this instructable, i cut myself last week and i couldn't advise you enough to ask a grown-up for help if you're not comfortable with cissors and metal (even if you are 26 like me ;))
And please excuse my style/orthographe : i did my best but english isn't my birth language ;).
Well, let's get started with these very easy steps.
Step 1: Find a soda can, a pair of scissors and let's cut the top of the can out.
Step 2: Clean cut of the top and cutting of the "petals"
The tip to achieve that is to pinch the can to mark the two opposite sides and then cut the remaining side in 2.
May not be clear, but i think that images are self explanatory.
As soon as you cut the side following halves, quarters and heights, you should get 16 petals that we are going to spread out.
Step 3: Spreading and folding the petals.
To be able to "finish" the folding of the whole petals, remember not to mark the fold of the first petal (so that you can insert the last one underneath).