Every house needs a site.
Sites generally come in two
flavours, vacant (i.e. land without an existing building) and built on.
Vacant
land can appear attractive as there is no existing house to demolish. However a vacant block does come with expenses. For
example, have boundaries been surveyed? Is there a stormwater and sewer that can be
connected to? Are the utilities (power/water/town gas) present?
Each of these items are potentially costly. For example the
water main usually runs under one side of the road or the other. If it runs along the other
side of the road from your property then you are looking at serious money for a connection. Imagine the cost of digging across the road (council approvals will be required at the very least), or engaging a specialist who can tunnel under the road.
If a sewer connection is not possible then you'll need to provide waste treatment to council standards.
If the block has an existing building on it try to get a quote for the demolition before buying the property. There could be hidden costs in asbestos, concrete slabs, basements etc.
Check the block for views, sunshine (orientation), or neighbours who can overlook your block (i.e. existing buildings with views in to your property.
Council should be consulted for zoning both of your property and the adjacent neighbours. You don't want find the neighbouring property has been zoned for commercial or industrial use once you've started building!
Finally, if you aren't familiar with the suburb do the normal checks on access to schools, public transport, shops etc.