I was looking at how master Korean players played fiddlesticks support, and these were a couple of builds with a decent win-rate.

win rates of each player as fiddle support ranged from 60% to 25% but these were the two builds that had <50% win rate. Full support was 33%.

The items are listed in their purchase/completion order.

Most players will skill E->Q->E->W/Q then max Q -> E-> W , but some of them will put one point in E and Q and Max W first. It depends on your playstyle of either peeling as much as possible with E/Q or going aggressive with W.

Mastery-> These were all over the place, for the most part the higher AP builds would use Thunderlord's Decree and this was the most popular, some mixed AP/Tank builds use Deathfire Touch and full support would use Courage of the Colossus

The only other boots I saw used were CDR boots.

Ignite was the most popular summoner followed by Exhaust , but this depends on your team composition.

Runes were more or less the same with the exception of the full support style of play which only took defensive stats.
9x Armor red
6x MR blue
3x Scaling MR blue
9x Scaling Health Yellow
3x Quint of Movespeed

Remember to do support things, AoE silence when you get dove, fear assassins/adc in fight. Roam mid if you can and use your ultimate. Stay alive, casting W will likely do next to nothing if you have few points in it and few items, it just makes you a sitting duck.

Or just play Janna instead