A method of sizing of a stent graft (20) including placement of fenestrations (30, 32) to ensure access to side branch vessels (13, 15) through the fenestrations when the stent graft is introduced into a body vessel and an assembly method for a stent graft including temporary diameter reduction arrangements to enable partial release of a stent graft to assist with positioning of fenestrations with respect to side branch vessels. The method includes spacing the fenestrations to be the same circumferential distance as the side branch vessels irrespective of the diameter of the stent graft.