A roof (1A; 1B) for a building, the roof comprising: a ridge beam for defining an upper edge of the roof; a first eaves beam (18a, 18b, 18c) for defining a lower edge of the roof; a first panel (56a, 56b, 56c) connectable to both the ridge beam and the eaves beam (18a, 18b, 18c), and being capable of spanning the distance therebetween and extending over at least a first portion of the area of the roof; and one or more retention structures positionable relative to the first panel (56a, 56b, 56c) and one of said beams (52; 18a, 18b, 18c) and configured to clamp said panel (56a, 56b, 56c) against the other of said beams (52; 18a, 18b, 18c), wherein the or each retention structure further comprises a first strut member and a second strut member, each strut member (70, 76) having a first end (72; 78) and a second end (74; 80), wherein the first end of the first strut member is adapted to be coupled to the first panel (56a, 56b, 56c) and the first end of the second strut member is adapted to be coupled to the beam (52; 18a, 18b, 18c) relative to which the retention structure is positionable, wherein the first and second strut members (70, 76) are hingedly attachable to one another about their respective second ends (74, 80) by a pivot, characterised in that the or each retention structure comprises a mechanically-operable jack mechanism configured to urge apart the first panel (56a, 56b, 56c) and the beam (52; 18a, 18b, 18c) relative to which the or each retention structure is positionable, so as to urge the first panel (56a, 56b, 56c) towards the other beam (18a, 18b, 18c; 52), and in that the pivot is operable so as to urge apart the first ends (72, 78) of the strut members (70, 76) to urge apart the first panel (56a, 56b, 56c) and the beam (52; 18a, 18b, 18c) relative to which the retention structure is positionable, or to urge the first panel (56a, 56b, 56c) and the beam (52; 18a, 18b, 18c) relative to which the retention structure is positionable towards each other. a ridge beam for defining an upper edge of the roof; a first eaves beam (18a, 18b, 18c) for defining a lower edge of the roof; a first panel (56a, 56b, 56c) connectable to both the ridge beam and the eaves beam (18a, 18b, 18c), and being capable of spanning the distance therebetween and extending over at least a first portion of the area of the roof; and one or more retention structures positionable relative to the first panel (56a, 56b, 56c) and one of said beams (52; 18a, 18b, 18c) and configured to clamp said panel (56a, 56b, 56c) against the other of said beams (52; 18a, 18b, 18c), wherein the or each retention structure further comprises a first strut member and a second strut member, each strut member (70, 76) having a first end (72; 78) and a second end (74; 80), wherein the first end of the first strut member is adapted to be coupled to the first panel (56a, 56b, 56c) and the first end of the second strut member is adapted to be coupled to the beam (52; 18a, 18b, 18c) relative to which the retention structure is positionable, wherein the first and second strut members (70, 76) are hingedly attachable to one another about their respective second ends (74, 80) by a pivot, characterised in that the or each retention structure comprises a mechanically-operable jack mechanism configured to urge apart the first panel (56a, 56b, 56c) and the beam (52; 18a, 18b, 18c) relative to which the or each retention structure is positionable, so as to urge the first panel (56a, 56b, 56c) towards the other beam (18a, 18b, 18c; 52), and in that the pivot is operable so as to urge apart the first ends (72, 78) of the strut members (70, 76) to urge apart the first panel (56a, 56b, 56c) and the beam (52; 18a, 18b, 18c) relative to which the retention structure is positionable, or to urge the first panel (56a, 56b, 56c) and the beam (52; 18a, 18b, 18c) relative to which the retention structure is positionable towards each other.