Can/would you supply any more details, aspect, climate, and by dual living you mean accommodating 2 generations of family and not selling,

Houzz is extremely lucky to have an amazing contributor who draws floor plans which can take many hours and at no cost to you. You will find this very helpful being able to make a joint effort and also allowing you to see how furniture will fit cheers

Hi audrey67, should also have asked for front and side set backs which are allowed by your council

I would suggest you start looking at the volume builders floor plans and see if you can find one that is suitable and have them construct it. Very cost effective if the site is straightforward.

If the site and council area is complex then you'll need to engage a professional designer, architect, building designer or a design focussed draftsman. The more complex and difficult the more you'll need an architect to assist.

I can see some sense in what MD is suggesting re the volume builders, but you could also work with Clever Houzzers to "Mock up" a floorplan to what you would like to see in this building. This will save you a lot of money and when you think you have what you like you can then take these drawings to a Drafts person to finalize and deal with council. Why don't you try, don't be afraid to give it ago, we're here to offer our help.

I would start not from floorplans but from what control plan applies to you site first.
Otherwise you will be wasting a lot of time going nowhere

Thanks for the comments everyone. They are all good advice. Who is the best person to engage with respect to what can and cannot be built on my property and where the building can and cannot be built on the block. I am in Brisbane city council, but my block is classed as Low Density. It is on 607square metres. People around the corner from me live in a duplex on 540sqm block. I have both a 200mm stormwater pipe running across my property and also at the back, a sewer pit. Therefore, there will be some restrictions, but not unsurmountable ones. I have been told by the people in the duplex who has also just build a duplex, that I would be able to build dual living on my block, My nephew has also said that he would be keen to rent the second duplex from me, if I were to live in one. I don't intend to sell the property ever if I can help it and so I would probably remaining living in one of the accommodation. The place has nice view at the back which is South. Has North aspect at the front. New neighbours are currently building a huge house on the East side which has 6 metres of it being built on the boundary fence and their house will have a 4.5 metre setback. The suburb is a changing one and is 5km from the city. I don't intend to progress this project for another 5 years, but would like to do all of the research, cost estimations, now to determine whether it is even worthwhile doing. I wouldn't be surprised if by then, the zoning had changed even if, for now, the site is only low Res A building. I can interpret most of the BCC codes etc, but I would prefer to engage a professional for this early stage to get a big picture idea of what is possible. I have seen a lot of companies that have dual living house plans, but they are all lowset and because I have a highset postwar house on one side and a huge modern brick and rendered double storey box going on the East side, then I don't want a lowset that loses all the nice breezes that I get now. I may lose them anyway when the new house is built, but I have had a little house before in between two double storeys and a lot of breeze and privacy is lost.

You'll need to engage a professional design consultant, architect, building designer or a design focussed draftsman. Choose one that has local knowledge and has experience with dual occupancy.

Hi Audrey, I'm in NSW so things might be a little different however, your local Council should have a duty planner, or you should be able to make an appointment with a planner to discuss your plans. This will give you a general idea of what is possible and best of all, it's free!

Go to the Brisbane city council. Meet with a person from their residential planning and building department. They will give you the rules, regulations, set backs required for your home, with your size block. Then you have knowledge to take to a professional. Have a read of https://www.brisbane.qld.gov.au/planning-and-building/do-i-need-approval/residential-projects/dwellings