Green’s Dictionary of Slang

saga adj.

also sagger
[SE swagger]

(W.I.) fashionable, showy, garish, over-dressed.

[WI]P. Sherlock West indies 143: Saga boys dressed in sheath-like saga pants, ‘peg-top trousers’ and saga coats called Bim-Bams.
M.P. Jones Jouvert Morning 83: He developed an absorbing interest in the most bizarre clothing: bright ties and saga cut trousers.
[WI]Allsopp Dict. Carib. Eng. Usage 482/2: saga (sagger) adj. [...] [Of dress, esp. men’s] Very fashionable and showy; over-stylish, garish.

In compounds

saga-boy/-girl (n.)

(W.I.) a young person who adopts a particular style of dressing, e.g. tight-waisted jackets and peg-top trousers.

[WI]S. Selvon ‘Great Drought’ BBC Caribbean Voices 19 Oct. in Selvon (1989) 88: No trouble here, no steel band and no saga boy to humbug yuh.
see main sense above.
[WI]R. Abrahams Man-of-Words in the West Indies 125: A sporty fellow is generally admired [...] but he must know when it is appropriate to be sporty. He therefore runs the risk of being branded a saga boy.
[UK]R. Antoni Grandmother’s Erotic Folktales 188: Pompous was Mistress Matilda / And haughty she was lovely! / Sagaboys tried to no avail / Bigshots tried and they too failed!