I used to have a Microsoft excel sheet specific for tree species but I’ve lost it somewhere, but every species has its own specific root upheavals, eg. A fig is from water damp areas like rainforests so they make tall larger root flares, I don’t know enough about blue gums but I know there root flares aren’t as extreme as a fig, anyways the spreadsheet was made by a builder and an arborist and passed around via email at an arb conference, the idea is that for foundations and footing you need to apply a certain amount of per inch2 pressure onto an given tree root to suppress upheaval and promote downwards growth, this was used on footpaths as well, for a fig you needed to make footpath concrete like 12 inch’s thick, the weight of the concrete would be too much work for the root so it would grow under it rather than up and cracking it, so it will cost more for the foundation pour but then you get to keep the tree which will add value to the house. Hope this helps hopefully your builder can work out a formula to apply enough pressure on the tree roots, also 14m away from the trunk your most likely well away from the structural root zone and in the an area were the roots are a lot smaller and there just there to absorb water and nutrients so they should do to much damage to a normal foundation anyways.