I was browsing images of Hawaiian petroglyphs the other day, and had a thought. We know the Hawaiians created them. We know the Hawaiian language. We know that many of the petroglyphs represent known concepts.
So, why not use those glyphs to derive a Hawaiian writing system? Sounds fun!
I then sat down with the web on my computer and a very thin tourist-friendly guide to the Hawaiian language, and in no time I had a serviceable first draft. I did it by taking the first sound in a word that has a corresponding glyph, and simplifying or stylizing the glyph a bit, and so I had an alphabet.
For example, the fishhook glyph. I forgot its name (it looks a bit like a capital letter J). I used it to represent the first sound in that word.
After that I tried to build a syllabary, because Hawaiian has no consonant clusters at all, but didn't have enough glyphs or words at hand. But anyway, alphabets are an order of magnitude easier to learn.
If I get the time, I will put my alphabet online as a font.