Hi! I'm new to single speed bikes but I do a lot of work with building and fixing bikes so I'm looking to build my own single speed bike. Looking for everyone's opinion about what parts are best for a single speed bike (aka what do you prefer--for example: what frame type, bars, for, cranks, tires, seat, etc.)

a road frame with a horizontal dropout, but if you can, try getting some track specific frame, might pay off when you want to try out fg.

you are going to get plenty of different opinions on parts, so I'll let other members raid you with their recommendations.

Frame: I have an old, lugged, road conversion. I like it, not too heavy, geometry fits my style.
Bars: I currently have bullhorns, I use bullhorns because I climb a lot of hills and I find the bullhorns give me the best leverage to do so.
Forks: Stock fork that came with the bike, nothing special or anything.
Chainring: Blackspire MonoVeloce, I've had them for a long time and they are quality made. Really round, tough, and I like them.
Cranks: Shimano 600 road cranks, and they're just cranks.
Tires: Gatorskin on the front and UltraRace on the rear, I've yet to have a flat on either of them.(knock on wood) They aren't the fastest rolling tires but they roll fast enough for me and they are quite puncture resisting. Since I am not exactly racing or anything, I'd give up a bit of rolling resistance for a more puncture resisting tires.
Saddle: Fizik Nissen, they are comfortable for me, but maybe not for you, different asses prefer different saddles.