Knock down extension and redo

Hi There,

I am new to this forums and I am am hoping to get some general advice. I am looking to potentially buy a house, a large part of that is pending on whether what I am looking for is possible. I know everything is possible but within reason (cost of course).

What I am looking too is knock down the current upstairs extension, as this only takes roughly 1/3 of the downstairs portion of the property, ideally I would like to have an extension that is taking up near 100% of the downstairs foot print. I realise some of the living area may not be practical thus getting me closer to 90% of the actual downstairs footprint.
(see attached image for floor plan)

So to get to the point what I am looking to understand is this possible? If so are there any yes but... if so what are the considerations it might hinge on?
Also if anyone has any experience on the cost of something to this effect as a ballpark. I know that there are an extreme amount of variables to consider but I don't mind if its + or - 30% it gives me something to work with.
The area of the extension would be roughly 8m (width) x (length) 11.7m (93.6 m2)

 

Don’t take these numbers as being correct. But essentially you are trashing say, $50K worth of 2nd storey extension before spending $150K for your ideal extension. Yes you can possibly do it but value-wise you have lost $50K + any overruns and contingencies that you run into building the new extension you plan.