How to build:

Had a colleague who commuted from Herford to Paderborn daily - he described his vehicular transport as a "Shed"  
as usual Scaleys  cannot spell: Nissan - which may have been slightly better appointed than a shed.

How to build a:

A Nissen Hut

https://www.derelictplaces.co.uk/threads/how-to-build-a-nissen-hut-2021.38472/



now on the look out for Anderson Shelter (https://andersonshelters.org.uk/design-construction/)
and Romney Hut and
other period pieces
(Watched a UK TV programme where a "Utility" piece of post WW2 furniture was converted into a "Toy Box on fun bowling ball feet" sold for 250 quid!  My parents had one from their first home - it was a 2 drawer Tall Boy then! and cost around 30 bob.)

There are more as those who consult:
https://andersonshelters.org.uk/other-shelters/morrison-shelters/
will realise!
and
https://andersonshelters.org.uk/other-shelters/stanton-shelters/
and
https://andersonshelters.org.uk/other-shelters/concrete-shelters/
and
https://andersonshelters.org.uk/other-shelters/wilmot-shelters/
https://www.northumberlandgazette.co.uk/news/deluxe-wartime-shelter-uncovered-in-back-garden-414354
and
https://en.wikipedia.org/wiki/Romney_hut
and
https://en.wikipedia.org/wiki/Quonset_hut an american import.