Do yoiu mean a wrap out of the supermarket that youre gonna fill yourself, or a pre-filled one?
The wrap itself will be 1 syn per 20 calories as theres no free food. The lowest syn one I know that is of a sane size of is the Weight Watchers one which is 5 syns. There are lower ones but theyre tiny, not much use for a real wrap. Most of them are around 7-10 syns.
Just to back up what Erm has said really, only the Weight Watchers tortilla wraps are 5 Syns. Other wraps can be anywhere between about 7-10 Syns each!
Really, if you want to maximise your chance of weight loss, and stick to the plan properly, you should be Synning them as 1 Syn per every 20 calories.