Haugesund airport Karmøy, or any major Norwegian airport.
By car from:
E 18 towards Drammen, over the bridge, turn right onto E 134 direction Haugesund. Follow this for four hours through Kongsberg, Notodden (tasty burgers at Hydro Texaco by the roundabout), Vinje, Haukeli until you see Røldal at the end of the tunnels after the Haukeli mountain pass. App 4,5 hours.
Follow E 16/Rv7 to Kvanndal, car ferry to Utne, Rv 555 to Odda, then Rv 13 to Røldal. App 3 hours.
E 39 to Aksdal, then E 134 to Røldal. For a scenic route, aim for Rv 13. App 3 hours 15 min.
Follow Rv 9 until you reach Haukeli, then turn left. App 4 hours.
Follow E 134 to Røldal. App 2 hours.
By Bus :
http://www.nor-way.no Nor-Way Bussekspress has options from many Norwegian cities.