Sell the backyard? CGT?

Hi all,

Looking for some guidance on buying a house on a large block,subdividing and reselling the subdivided land to recover some initial outlay to create +ve geared property from original house.

So have many people on here done this?
Good or bad experiences?
Anyone know what the CGT implications are on selling the land without the house on it? ie how do you work out what the gain is for tax purposes?
What are the gotchas?

Thanks in advance.