Noa is a boys name in Wales (pronounced Noah) but a quick google search has revealed that it's commonly used as a girls name. What do you think of it for a boy? We prefer this spelling as we are Welsh.
Noa seems a bit feminine, I much prefer the Noah spelling. Plus, though you might not mind spelling Noa's name all the time, he might! Although, if it is important to you to spell it 'Noa' then go for it, it's still a nice name.