attached bolted durability durable firm frame gray grey roofing see-through steel steel roofing frame strength support trusses architecture background construction glass metal modern roof structure ceiling elements England english form girders Great Britain iron London Marylebone railway station transport angle-iron angled angles bolts braced bracing building building-construction building-site building-work color coloration colors colour colours connected connecting constructing frames framework house joined light metalwork New open preliminary-framework reinforced reinforcements reinforcing secure shadows solid space spacious strong sunlight unfinished black-and-white buildings cambodia concrete construction-work dangers daylight distance distant galvanised galvanized greyscale metalic monochrome multi-storey multi-story people ribbed ribbing risks risky roof-trusses safety sheeting sheets shelter sheltered structural-work upper-storey upper-story workmen