Strange construction type

Found a reasonable priced terraced property with a great yield of 8-8.5% yield in Glasgow.

I've received Homebuyers Pack and in additional comments it states construction type is

Blackburn Permanent III.

I can find detail about Blackburn Permanent II which states concrete prefab but I can only find limited info regarding III. It would appear III is brick shelled but the roof is metal.

I've never heard of a metal roof or Blackburn Permanent.

Any ideas if property would be suitable for a BTL mortgage?