the roof structure 22 of the enclosure 10 as shown in fig6 a cross beam channel 40 is interfitted onto and supported atop the upper lateral horizontally extending edge of the wall panel 24 further window framing 28 is thereafter supported atop the cross beam channel 40 as shown in fig7 a cross beam channel 40 is interfitted onto the lower lateral horizontally extending edge of the wall panel 24 further window framing 28 is thereafter abutted against the cross beam channel 40 in a manner described in connection with fig5 the upper track 38 b and strand 94 are shown in relation to the roof structure 22 as shown in fig8 the upper track 38 b of the right wall 20 is shown supporting the roof structure 22 the right wall 22 includes an upper track 38 b a wall panel 24 and window framing 28 because the upper end of the right wall 20 angles upwardly and is supporting relation with the bottom surface of the roof structure 22 the support strand 94 is not needed further the base portion 74 extends in a direction outwardly of the enclosure 10 as shown in fig9 an i beam 36 is shown separating two window framing sections 28 and l shaped flanges 90 are connected to opposite sides of the central body 60 extending between the flanges 62 and 64 of the i beam a closure member 44 is inserted into at least one of the two opposed squared c channels 63 and 65 of the i beam thereby providing a flush surface with the.