Assuming you have square taper bottom bracket? Is this a budget build or are you trying to do it right? Really, your only option to do it "right" is to replace the cranks with some that will accommodate a single speed chainwheel, although this shouldn't be a big deal. Look for used track cranks, or used middle of the road MTB or road cranks also. Surly and Salsa both make some nice SS chainwheels IIRC but the trick will be finding a crankset to work with your frame and bottom bracket spindle length without being able to try them out. Although if you get a used triple crankset that would give you three possible positions to place a chainring for best chainline and frame clearance.
If this is all news, it may be beneficial to stop by your LBS and speak with the mechanics for a while. I know one of the things many people, including myself, enjoy about a SS conversion is tinkering with it to get it "just right." Of course, if you don't have a parts stash yet, you will after a while!