This luthier have been building some ukes and they are great.
Glad to hear this Fernando - then you should be fine. As Phil & Eric pointed out, Redwood is also a great option, but I'm guessing you'd have to have it shipped in. At least in Central America, where we build, no one uses it (yet).
But for a hardwood top (and an instrument that would use all native woods), Spanish Cedar, or as Fernando and I say,
"Cedro" is really hard to beat. To me, it is one of the three fundamental hardwood soundboards, along with koa and mahogany. You have Myrtle (am not familiar with it), and Monkeypod (fabulous stuff!) now making waves, but of the three traditional woods, Cedro has probably been in use the longest - Cuatros go back 400 years or so. I am always amazed this wood isn't better known outside Latin America.
It can come in straight grain, like the aforementioned cigar boxes. I think this might look great paired with the figure of your rosewood body. If you're looking for more beautiful figure, however, one with a different form than rosewood grain, take a look at these old photos I dug up:
The first is our longneck Concert, the second is a pair of longneck Sopranos. We built a series of instruments out of this board. This kind of figure in Mahogany is called "plum pudding". Cedro also has a lot of other beautiful figure patterns, often similar to Mahogany.
As far as sound, it is unique. Not overly loud, yet on larger instruments it can be somewhat percussive. The term that has most often been used to describe it, however, is "sweet". The sound is truly lovely.
Let me put it this way. You may have heard of Chuck "Frets" Fayne. He's one of the world's foremost collectors of ukuleles. His collection, as a matter of fact, formed most of the basis for the book: "Pictorial History of the Ukulele". He does a column over at FMM called "Uke Yak", on vintage instrument identification. He's also a sneaky-good player.
He has one of these Sopranos (or another one from the same board - not sure). While sound is always subjective, out of his 500 or so premium ukuleles, this Cedro-topped instrument is his favorite.