Time for some hare brained architecture!
I was thinking about elves living in their tree houses via the mapping of such inherently three dimensional settlements. Normal houses transplanted from the ground is unsatisfying. Using magic to shape the trees feels like a cop out and is kind of dubious biologically. It is possible, trees are fairly robust that way, but just seems risky for a race of tree-huggers to do on large scale.
So I though about houses suspended by ropes going criss cross between the trees. You'd put webs between the ropes to create level load bearing surfaces for floors and pathways. Textiles would then supply protection from elements in the form of floor, walls, and ceilings. Treatment with oils or tree saps would allow water and wind proof surfaces.
Then I started thinking about the sheer amount of fiber needed for all that. It would be light weight, but you would need lots of it. And such structures would require constant rebuilding, so the demand would be constant.
Where would elves get all that fiber? Steal it from the giant spiders? Fill the ground below with cotton plantations tended by human slaves? Raise monkeys with sheep like fur? These ideas have some flavour and might make interesting stories. An elven settlement surrounded by a forest absolutely filled with spiders and their webs makes lot more sense if you can point out that the spiders are farmed for their silk by the elves.
Still scaling these solutions up would mean meddling with local ecology on the same scale as human practices did. It doesn't really give the elves a flavour of being more in touch with the nature.
So I ended up with a source of fiber that automatically scales up with the population and thus presumably the demand. Hair. My elves will simply grow hair suitable for ropes and textiles at a speed sufficient for the demand.
Using homes build from parts of your own body should also be convenient when adding magic. Such self-sourced textiles would also be good for magically attuned clothing and various magic talismans. This would help in making the elves inherently more magical than humans, something that many settings seem to struggle with. And elves traditionally come with exotic hair colours...
But what about the practical issues? Such buildings should be mainly require tensile strength. (We can at this stage hand wave weather and wear resistance.)
What level of tensile strength would be needed for such structures? Reasonable changes to design from one described above to reduce loads should be assumed.
Can hair provide the needed tensile strength or is something more exotic needed? Some spider silk can be added, if necessary.
What kinds of loads would the trees be subjected to and could trees withstand the load? Feel free to assume the most sensible trees and forest type.
