Ah, I don’t believe the stonemason would place all of these items my initial feeling is that the stonemasion creates the blocks/ resources which your workers then place wherever you designate; just like the carpenter right now.
I obviously don’t know what the team are planning but I imagine the first ‘tier’ wall to be a really basic stone wall which is simple made by the stone you ‘harvest’ and then placed by your workers. Your stonemason could turn this stone into a higher ‘tier’ depending on how the game handles that, and then create the improved stone wall blocks as well as the other stone objects mentioned.
Well, arguably if roads enable your settlers to move around the place faster they would definitely serve a massive purpose in larger settlements :P. Either way I feel like the workers would be able to handle the construction of roads.