I’d normally gravitate towards using line plane intersection but it could become a nuisance when using an orthographic camera (are you going to?).
Instead, you could opt for something along the lines of:
- a plane that moves with player, ignoring all collision but
Visibility(or whichever channel you’ll dedicate for tracing) - ideally, you’d make a unique object channel - set it to be not Visible; showing it here to demo
Placing blocks:
The layer can modified with RMB: