WIY – the Rambam’s Shittah is quite clear in Hilchos Teshuva as well as his Hakdomo to Perek Chelek, that Olam Haba is a purely spiritual place that exists in PARALLEL to our current reality. Mashiach is not a supernatural occurrence, and will happen in this world. In fact, the Rambam says quite clearly that Moshiach will die.
The other approach (that of the Ramban and Raavad, and Ramchal, and pretty much anyone who subsribes to Kabbalistic thought) is that Olam Haba is a new, physical reality which will replace our current world, i.e. that Techias Hameisim is the starting point of Olam Haba. At least this is how i understand it.