Crossword Genius

Welshman's building a platform (4)

Ross

I believe the answer is:

dais

I'm a little stuck... Click here to teach me more about this clue!

'a platform' is the definition.
(I know that dais is a type of platform)

'welshman's building' is the wordplay.
'welshman' becomes 'Dai' (Welsh name).
'building' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'dai'+'s'='DAIS'

Can you help me to learn more?

(Other definitions for dais that I've seen before include "stepping up here?" , "Raised floor" , "Platform; podium" , "Welshman's" , "support for speaker" .)

I've seen this clue in The Globe and Mail.
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