How long since you made the last changes?

There is a delay between getting crawled to getting indexed to getting updated in the SERP... as much as a month.

One more thing to check: Do an exact-text search for some phrase on your home page. Not the sitename and not the meta description but some text that occurs in the body of the page. That's the Bing computer's chance to say "Oh, whoops, we do know about this place."

whilst building it had a noindex meta tag. Bing had crawled it and showed message "We would like to show you a description here but the site won’t allow us."

That seems backward. The "we can't show" message is for when they haven't crawled--and if they don't crawl they will never see the noindex meta. Which, clearly, they didn't, or the site would not have come up in search. Have you seen bingbot visits in logs?

How did you get it to come up in a search: by words or the site name? (Bing seems to be fonder than most of exact-match names. My test site is roboted-out but it's got a plain-English name that could theoretically come up as a search query; in fact I get occasional visitors from Bing search but not from anyone else.)

Thanks I contacted Bing Support and they just advise to wait so we'll see

Bing will crawl any website faster than Google webmasters and getting rank in Bing SERPs is easier than Google SERPs. I experienced it. Coming to your issue, time does matters. Since, how long you are doing seo, or when you submitted your site to bing? Do you have any back link strength or social media activity? Do you have any crawling errors? We need to check all these things.

3zero, can I just check with you something?
That message you see, ""won't allow us" etc., is that for HTTP or for HTTPS home page?
I wonder if it's still thinking that HTTP is your home page and hasn't yet discovered the HTTPS home page, replacing the earlier HTTP? If you get my drift.

Have you got any kind of redirect on your crawled pages pointing direct to HTTPS? Try putting one link to https://www.example.com/

One other thing you could do is to make sure that the home page has some updated content, and not just the same as the original HTTP home page.

Thanks guys, still no homepage :-(

site is 4 weeks old
approx 93 links (mostly off press release to say we launched)
Facebook 500 follows, Linkedin 1600, Twitter 3000+
Redirect for homepage to https in place
SNI changed to dedicated cert as Bing seems to require whitelist for SNI
Homepage updated with fresh content every two days
All other pages indexing ok, homepage not to be found, do not even get the message now

Thankyou

Has the bingbot been crawling? Does it get a 200 response?

What happens when you do an exact-text search on bing? No match at all? (This is of course assuming there is something on your home page that's unique to your site. Paradoxically, the home page may be the least likely place for unique text, so the test won't always work.)