I love this swimsuit, I reckon it's 1950s judging by the fabric, cut and the fact that it's a one piece. I'm not if it is homemade or not, I suspect it probably is as I haven't photographed a label. I love the nautical print and the rope tie so kitsch!
And here's the ad..!!! Jantzen are an American swimmwear producer, Jantzen costume were sold in the UK too in major department stores. Haven't properly worked out who would of purchased their garments, but I reckon it's more middle and upper end as they aren't found in the mail order catalogues here.