The basic decorative possibilities of slate had been established centuries before their various manifestations in the architectural fashions of late 19th- and early 20th- century Canada. Simply, the appearance of a slate roof might vary according to the nature of the material itself or the way it was cut and applied. Size, thickness, colour and cut were four main factors that determined effect. Around one or more of these features developed the trends in slating associated with different architectural styles in Canada from the mid-19th century to the 1930s.
Slate size refers to the rectangular size, split and trimmed from the quarry slab. Historically it ranged from as small as 11 inches by seven inches to as large as 36 inches by 24 inches.
| Name | Length | Width |
| Doubles | 13″ | 6″ |
| Ladies | 16″ | 8″ |
| Countesses | 20″ | 10″ |
| Duchesses | 24″ | 12″ |
| Welsh rags | 36″ | 24″ |
| Queens | 36″ | 18″ |
| Imperial or | ||
| Patent slates | 24″ | 30″ |
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