gloomy mica
This was mentioned in another post but I wanted to expand on it because I think it would be both easy to implement and a very easy to use tool when building.
When building you can press and hold a key. This will lock the orientation of the block you are trying to build with. This way you can orient a block naturally using another block somewhere else then just press the key and place the block where you want it. Also allows for quickly building multiple blocks with the same orientation in places normally not possible. An orientation "picker" key may also be a viable way of doing something like this but I'm not sure if that would be as seamless. Would be good for slapping together a bunch of say slopes in a line quickly though.