Worry about designing and finishing a game first.
He already has. Several in fact. The one I have in mind is very good. If you mean finishing the game you want to be cross platform, that's completely counter-intuitive. Code first, plan later is a recipe for disaster.
gman has actually put a lot of effort into getting his irrlicht module working on the mac without success so far.
Sorry, I didn't realize that. Well perhaps Ogre then. Good to see you're around though. I'll go check my inbox.
Beside of that i never wrote a wrapper for blitzmax (How does this work?)
It's pretty simple. Just a case of writing C functions which receive an object ( Byte Ptr in BMax ) and then using the methods or properties of that object and ( if required ) returning the result. Then calling them from BlitzMax, perhaps creating a type in BlitzMax and creating methods which call those C functions instead. But it's not what I was suggesting.
i don't wanna do this kind of work and maintain it. I would prefer paying some amount of money and use an engine instead.
I wasn't suggesting that. I was thinking in terms of just making GMan's wrapper work on the Mac. But if it's not easily done ( and if GMan can't do it, it must not be ) then this is clearly a bad idea.