The installator informs about the space needs after these steps:
select packages / select dependent packages (*) / configure monitor /
configure graphics card / format (!) root / detect space need

- this procedure is very annoying while installing on a low-space-available
drive.

(*) the selection only selects 1st dependencies - please try to implement
some recursive algorithm to select all dependencies (example below)

package A is dependant on B, which is dependant on C

C <- B <- A

now: select A -> Install as well B
my version: select A -> Install B as well as C
right after selecting these, it would be appreciated to see what space is
estimated to be occupied