When building a house, there are consultants needed at different stages of the project. Some are always required, and some are optional at times. Below is a list of the common consultants that are engaged when building a house (note: there are more consultants that are used when building a commercial building, but this guide is focussing on building a house)

Building Designer / Architect:
Building Designers and Architects will assist you in expertly designing a building to meet your needs. They can submit the building design for planning approval ensuring it meets regulations, and also document working drawings (building drawings used for constructing the building), ready for obtaining a building permit. They have the knowledge and experience to not only design a building, but ensure it meets all planning and building codes and regulations, and will liase with other consultants to ensure everything ties together in the design and construction. They can engage all relevant other consultants so you don't need to hire each consultant yourself individually. Their services can be basic drawings for a building permit, to fully specified in every detail, including interior design. (To see types of drawings are used in a set of building plans, click here)

Note: A building designer or Architect is not required. Legally you can draw your own house plans, but if it is a complex design, it may well be worth investing in expert advice and services for peace of mind.

Land Surveyor:
A Land Surveyor is often used to take what are called levels of the building site. A 'level' enables the designer to understand the topography of the land, and determine the steepness of the slope across the site. This is particularly important on building sites with a steep slope. This information is useful in both design of the building as well as selecting the best construction method for the footings. Land surveyors can also take heights (levels) of adjoing buildings which is crucial sometimes when designing your own building to see how your proposed building may impact adjoining properties.
They can also establish the title boundary on the drawing which clearly shows the offsets from fencelines or structures that may encroach on your land.
They also can setout the hurdles used for setting out the building location accurately.

Land Surveyors provide a drawing of the building site with levels and can setout hurdles accurately.
Note: A land surveyor is not always required.
For more information on reading a Land Surveyors drawing and understanding levels, read here.

Geo-Tech Engineer:
This type of engineer takes soil samples from the building site to determine the sites Soil Class. This is important in determing construction requirements of the footings system. In a lot of cases, a building designer can use this informaton in conjuction with applicable Australian Standards to determine the construction requirements of the footing system. Where this is not possible, a Structural Engineer will use the Geo-Tech report to ensure the appropriate specifications for the footing system.

Geo-Tech engineers provide a report and basic plan of where the soil sample(s) were taken.

Structural Engineer:
This type of engineer is typically responsible for specifying the structural member sizes and grades of beams, columns, lintels, footings, rafters, purlins, studs, retaining walls etc. They are not always required depending on the house design and materials used in construction. In many cases for timber framed houses, a building designer can use the Australian Standard AS 1684.4 - Timber Framing Manual.
On sites that have a bad soil class as determined by a Geo-Tech engineer, Structural Engineers are essential in the design of the footings.
They are also requred in most cases where steel beams, lintels and columns are required to ensure structural stability and correct structural member specifications.

Structural Engineers provide drawings of structural member locations on a plan and specifications. Sometimes they provide connection detail drawings where required. In cases where under-pinning is required, the will provide a staging plan too

Note: A structural engineer is not always required.

Building Surveyor:
This type of Surveyor is focussed specifically on the building itself and meeting regulations. Their role is to ensure the building design meets BCA / NCC requirements and compliance, and to ensure during certain stages of the construction of the building that everything has been carried out satisfactorily. Once the building is at what is referred to as 'lock up stage', the Building Surveyor will issue a certificate of occupancy if all construction requirements / compliance are met.

Note: Once a building surveyor has been appointed by you, their service cannot be terminated unless under certain circumstances as set out by the Building Commission. Be careful who you choose, some Building Surveyors I have encountered have made life hell with over the top requirements which you must meet if that is what they ask for.

Note: A building surveyor is always required.

Energy Rater:
This consultant ensures the design of the building meets current energy star requirements. They use special software to determine all aspects of the buildings design and thermal performance, taking into consideration materials and insulation types used in the design and specification of the building.

Energy Star Raters provide you with a report of the buildings performance. If it doesn't comply, the preliminary report will make recommendations as to what is needed to make the building comply.

Note: An energy star rating report is always required.

Town Planning Consultant:
This is a specialised consultant that can assist in the design process before drawings are submitted to council for planning approval. They are experts in planning and can give design advice, work as expert witnesses in planning disputes, and can also assist with planning permit objections.

Note: A Town Planning consultant is not required.

Additonal Consultants (often utilised more in commercial buildings):

Mechanical Engineer:
This type of engineer has a varied role that goes beyond building. However in relation to a building, the Mechanical Engineer can be referred to as a building services engineer specialising in the Mechanical elements of the building. In this regard, the Mechanical engineer is concerned with designing what is referred to as HVAC (Heating, Ventilation, Air Conditioning) This includes duct work sizes, plant equipement, smoke exhaust systems, lifts, escaltors, travelators etc.

This type of engineer designs all electricals for a building, including ensuring adequate lighting levels are achieved via artifiical lighting for common use as well as emergency lighting. They design not only power and lighting, but also switchboard design, circuit protection, cable selection, telecommunication, stand-by power generation etc.

Hydraulic Engineer:
This engineer designs all hydraulic systems including sewerage and drainage pipework and hot and cold potable water reticulation.

Fire Engineer:
This engineer designs fire safety components of a building such as the sprinkler systems.

In addition to the information I provide for designing and drafting your own house, I have another side project that tells you how long a house or land has been For Sale or Rent in Australia.
It is also Free to Use and also has a search to give you a price range indication of house and land for sale that doesn't have a listed price.
It is called Get House Date www.gethousedate.com.au Mobile Friendly too.