With so many new estates around the outer suburbs there is plenty of competition between the land agents for your custom. This can lead to numerous problems due to many agents being focussed on their bottom line. 

For example they may not mention factors like fill and the (fall) slope of the land which can add costs to your building project. When purchasing land I would strongly suggest getting your builder involved before you place any deposits. A builder will be able to read documentation for the land and is qualified to comment on land purchase as well as understanding the pitfalls.