Writing him a letter is about the worse thing you could do (but I have a feeling you know that already). How awful would that be to see the guy the next day and have him completely ignore you or worse he might decide to have a word with you and say "sorry missus but there's no chance". Of course there's always the possibility that he'll come running into your arms, but for a bloke who's never given you any indication that he's interested, I don't think thats very likely. But, having said all that, you know summer is just around the corner (we hope) which is the ideal time for those lazy sunny afternoons sat in the garden (and hopefully there's just a fence between the two gardens that you can both see over or through. There's dozens of conversations that you can strike up, about the weather, about gardening, and as time goes on and you've picked up a few pointers as to what he's interested in Im sure the conversations will get deeper and a little more meaningful (perhaps). How hard can it be when you are both free and single? Slowly slowly catchee monkey! Good luck with it anyway!