I just googled & found this site, which quotes cost of R2.5 75mm. there are other suppliers as well. What was quoted to you for cost of roof installation, and was it itemised so you can see exactly what thickness the foil-backed insulation builder will use? I'm guessing the thinner (lower R factor). So, the new quote should reflect a credit for the cost of previous insulation, since it won't be used, then cost of thicker insulation added. Does that make sense? If you are unsure, best to speak with the builder. https://www.pricewiseinsulation.com.au/product/heavy-duty-fletcher-permastop/

To Modernise this without rendering or retiling the roof I would probably recommend to go darker with the trims. My top pick as a colour consultant would be Dulux's Domino for the trim. It will be a little bolder and create a more modern contemporary feel. You can see it pictured below as the trim. Obviously this house has painted their bricks in the shade "teahouse" however it will still look much better on your 1980s "peru" colour bricks! Don't hesitate to contact me if you need any more help colour wise!

Do you have any furniture you are wanting to put in there ? Does any of it have any colour ? I like the light floor colour , the rest let's just say it is a good neutral base . I'd start with a new front door -- a darker varnished ( glossy ) wooden door , or possibly even a blue to reference your outside . Then add colour via furniture ( or at least cushions ) , rugs , and artwork . Again , maybe several different blues would tie in with the floor , but also the exterior . If there are only blue exterior highlights , you may want to go for warmer colour inside -- reds , yellows , oranges -- again , ties in with the floor . To this end , I can't understand why people go with 117 shades of grey and offwhite and wheat -- live a colourful life is my attitude , as long as it is themed haha !

are the new sliding glass doors double glazed? are the original windows single glazed or in need of replacing for any other reason? do you hate the beige colour? how many of the old windows can be seen at the same time as the new doors? ... inside looking out is the most important view for me but what do you like the look of?