Hi Jorge.
Funny, I was reading through this thread for interest on the subject matter, thinking I might throw my 2c in... Only to see you've posted a pic of one of my builds! :cool:
With respect to your timbers however, absolutely go for it. There are heaps of timbers outside the traditions that will work and can look and sound superb. Jarrah has been used by luthiers before, as has Radiata pine. But to clarify, pines are not pines per se! There are more details to cross reference than just weight. Stiffness to weight ratio being a very important measure, cross grain stiffness etc. We are hard pressed in Australia to measure up to the standards many of the various spruces feature. Instruments have been built with Radiata, Bunya, Kauri, King Billy, Huon and many more. Some King Billy I've worked has had specs that match spruce, but that's hard to find now. Even within species, the timber varies greatly with some King Billy feeling dry and stiff, other pieces as floppy as cardboard. Great tone can be had from all, but it takes skill and experience to coax the best out of them when you are already behind the eight ball compared to other options. But perhaps that doesn't really matter in this case. Yours will have a unique sound, all your own and you made it! Likely that's good enough for now. In general my advice would be, try not to 'overbuild' - that's common when starting out, but ukuleles are usually best when light and responsive.
I hope it helps. Good luck and enjoy the process! Perhaps we'll see some pictures of your results in time.
Regards,
Jeremy.
J.F. Custom Guitars
http://www.jfcustom.com.au
Australian Guitar Tonewood
http://www.australianguitartonewood.com