Buying Land whilst renting our Main Residence and Taxes involved in doing this

Hi Everyone

Back again.  I have a question about purchasing land….. At present we are renting out our apartment which is covering more than our mortgage (yey).  We are living rent free at our inlaws while they travel for a few years (yey again).

I am keen to buy land to build on in the future.  What I wanted to know is does this change the type of taxes I pay.  See at the moment I am renting out our main residence.  I can do this without paying CGT as I dont own any other property and I lived in it for 18months before renting.  Would my situation change if I purchase vacant land?  We would like to buy the land and say build on it in 2years approx.  That way we can be paying off the mortgage on the land then decide if we need to sell our apartment to build or can we afford to keep it and build as well.  I know if I wanted to avoid certain taxes I would have to sell apartment before building or does that only change when house on land is at lock up stage?

thanks Kylee