Jeez -- you're braver than me ! Lets start -- you take off all the tiles individually , remove the wiring , remove the crossmembers and gutterings and old insulation and building paper , frame it higher , probably new crossmembers , reassemble , find new matching roof tiles because you can guarantee some won't survive , timber that matches , re-gib the inside ( possibly the whole walls depending on condition ) , decide if you retain the windows ( I suspect they'd look too small / low ) or new windows , and same with the doors . Repaint / wallapaper / maybe blinds . The materials more difficult than expensive ; but the labour would be expensive . And what do you end up with ? Not really much IMO . A taller version of a fairly plain 1980's house . That's a bit harsh -- it's going to be your home . And the cold-hearted ( haha ) part of me would ask will it make it worth any more ? Do you spend $50K ? Do you think you are getting a bargain and its worth it ? Do you pass on the house ? Do you modernise the whole house ? The house next door makes me think its in a 'better' neighbourhood , so maybe live in it for 2 or 3 years , and do a $200k remodel . Just doing that rear part doesn't strike me as a great idea ( unless you are all 2.4 metres tall haha ) , BUT then I don't know the whole story . . . . . . . .

assuming you don't have buckets of money i would paint the panelled walls white, have an electrician check all the wiring and add some cheap new plain light fitting and then live in the house for a while to see how it feels before you plan anything major

Is that those tiles ? I did up a commercial bar 15 years ago that had them , with all the little holes and things . On a budget of next to nothing , I cut plywood to size and varnished it , and replaced every 5th or 6th tile with these . Still pretty boring , and we had the luxury of height , but I then did more plywood pieces , 200mm wider and longer . Half these I did in a mid brown stain , the other half in a reddish cedar stain , added 4 downlights per panel , in holes drilled into these panels , and suspended these mostly 100-150mm lower , with polished stainless steel threaded rod .

Each council in Western Australia has its regulations for habitable rooms. These include ceiling height and window size. You must contact your local council to get the appropriate building certificates and approvals for your conversion. This is what my local council has on their website. https://www.canning.wa.gov.au/CanningWebsite/media/Files/Residents/Planning-and-Building/Information-sheets/BIS-22-Information-sheet-Habitable-Room-Conversion.pdf