A platform system useful for constructing, maintaining, or repairing greenhouse roofs comprises a platform section providing a working area surface formed with removable treads supported on left and right platform rails. The platform section is supported by downwardly projecting upper and lower support bases appointed to rest on structural members of the roof, thereby providing a clearance between the working area surface and the roof beneath. Guardrails extend along the sides of the platform section between guardrail posts attached at the upper and lower ends of the platform rails. The system is light-weight, minimizing the loading imposed on the roof and permitting it to be readily positioned by a small work crew. The support base may include retractable rollers that permit it to be slid upward across the eaves and onto the roof. A deployment assist cart may be used to erect, support, and access the platform system.