You are generally removing stuff when going from geared to ss/fixed, the only things I can think of that are ss specific are chainring bolts and chain. Having said that....
What kind of drop outs has the frame got?
If they're vertical it can be tricky to get chain tension without using a singulator type device. "Magic" chain length (a half link chain or even just a few links are useful here) or drilling/grinding a wee bit out of the dropout can work.
What cranks are currently on the bike?
You might be able to remove a couple of chain rings and save yourself the cost of a "dedicated" single speed chainset. Or just run whichever chainring you want, leaving the others on there.
What sort of hub/gear arrangement is on the current rear wheel?
As with the chainring, it's possible to leave all cogs at the back but only use one of them - if you're not running a dérailleur then whatever cog you put the chain on, it stays on. A single speed kit for a cassette rear hub costs about £20, it's just a cog with bigger teeth and some spacers. This lets you adjust the chainline too...
You are generally removing stuff when going from geared to ss/fixed, the only things I can think of that are ss specific are chainring bolts and chain. Having said that....
What kind of drop outs has the frame got?
If they're vertical it can be tricky to get chain tension without using a singulator type device. "Magic" chain length (a half link chain or even just a few links are useful here) or drilling/grinding a wee bit out of the dropout can work.
What cranks are currently on the bike?
You might be able to remove a couple of chain rings and save yourself the cost of a "dedicated" single speed chainset. Or just run whichever chainring you want, leaving the others on there.
What sort of hub/gear arrangement is on the current rear wheel?
As with the chainring, it's possible to leave all cogs at the back but only use one of them - if you're not running a dérailleur then whatever cog you put the chain on, it stays on. A single speed kit for a cassette rear hub costs about £20, it's just a cog with bigger teeth and some spacers. This lets you adjust the chainline too...