Whilst I have no true knowledge of this, I believe that a hay loft may have been pressed into service in the beginning. Because the sail makers use the term 'sail loft', referring to it as the 'Mould Loft' would signify what 'loft' someone was talking about. The mould loft is an area or as became the norm, a second story space usually over the actual building ways. The loft would be as free of posts, partitions or any other obstruction as possible. Large windows, especially north facing would be used.
Natural daylight is best.
The actual floor itself would be kept clean and as free from dings as possible. It would be painted an off white or very pale gray. No street shoes were permitted, either a pair of slippers or stocking feet were allowed. The lines 'laid down' were drawn in pencil and shoes could scuff them as well as track in dirt or grit. Try drawing a 'fair line' 60 feet long and hitting grit every so often.