Kind of hard to answer the first part of your question because the answer is what ever material is best suited to the current project
As I do lots of different types of project the list of materials is quite varied. If it's work for a customer then I might make suggestions on what to use but ultimately it is the customers choice
Again the second part of the question can be either or
Sheet materials such as plywood then I would obviously buy in, but if working with hard woods then I would do my own glue ups using what I had available to me generally.
If it is a wood project I am working on I generally use hardwoods & use what I can buy locally from a particular sawmill, they operate a sustainability policy & I tell my customers that I use wood that is supplied from a sustainable source. This does limit me a bit but I still have some nice woods to use. They generally stock Ash, Beech, Chestnut (different varieties), Elm, Hornbeam, Lime, Oak, sycamore & Yew. They also have a limited supply of other hardwoods from time to time
I tend to use more Oak than anything else, Hornbeam/Lime are very nice for 3D work as they are very dense, Yew is a stunning wood but tends to be a bit on the pricey side for me unfortunately. I am also quite partial to Elm but that can be a bit hit & miss when it comes to 3D work so doesn't get used much for that sort of job