Changed my single speed from flat bar to road bars. Got some brake levers on the tops and just got myself some new cabling. I just need the pads now and i'll be allllll good.
Although i won't be commuting to work on it anytime soon
What kind of brakes and levers? Some don't play well with others.
As FullMotoJacket noted you need to (should) make sure the flat bar brake levers have the same pull (assuming mechanical cable) as the calipers. Generally... (very generally, anyone please feel free to correct me if I have something off...)
Most road rim calipers (regardless of brand), road mechanical disk and old style mountain cantilever have similar pull (close enough) and are more or less interchangeable, but should not be used with the below.
V-brakes (linear pull) and mountain disk have different pull and they should not be intermixed with the above.
The newest higher end road groupsets from Shimano have a different pull ratios yet, and should not be intermixed....
Changing the pull ratio basically changes the mechanical advantage, when you intermix "incompatible" levers and calipers the brakes will not work as expected (too hard to pull, too sensitive, levers bottoming out unless the pads are very close to the rim, etc.), some do it and get away with it, YMMV. Personally I have experimented with it both ways (intermixing) and find the brakes usually suck, I consider it a safety problem.
They do make flat bar levers that work with most road groupsets, including older mountain levers for cantilever brakes.... they also make devices that change the pull ratio but it is easier and cheaper to use the correct levers.