ive used both sides and they do just fine,i prefer the white side,that doesnt look like foam board though,anyway,take condensation that the steel roof is gonna have,if you place the insulation right against it,it will mold,use clear plastic ,then your insulation then board,on the roof i wouldnt worry about reflection,just under the lights mate.
you will need some type of barrier against that metal though,it might be a year or so before you notice smell ,but take my word the metal will condensate,be like sleeping in a camper and waking up to sweat drops falling on you ,also being drenched