1) Whoever paid for the medication decides who lights the joint; no matter who rolled it.
2) If you do not roll pro-style, do not attempt to fake it! You are not going fool anyone with a shitty joint. You will however piss everyone off. Especially if it is the last of the weed! Admit you can not do it and let a pro take care of the rolling. A poorly twisted doobie can be a big downer.
3) If you did not pay for the herb, but rolled the joint, it is usually customary to pass the joint back to the owner of the meds for inspection. Usually the owner will take a look make sure everything is alright and then pass it back to the roller to light. Some people may light it themselves considering they did pay for the herb!
4) Do not brag about how great a joint roller you are because no matter how good it is you just sound lame. No one wants to wait for you to roll a perfect joint if it takes 25 minutes to get finished.