For future reference BIS ~ building is possible - no encroaching, materials are present, the belt is not too steep.
No need to choose whether you want to build a belt alone OR on a pillar OR on a stackable belt. Just pick "build belt".
If you need to build pillars or stackable belts, these options should remain as are in the game.
How it would work:
1) pick "build belt" from the toolbar:
A small icon in bottom right corner appears. It is either a picture of a pillar or a stackable (if researched). This comes into play later.
It would be nice if a number appeared of how many items per second the held belt supports. (60/s OR 120/s OR 270/s OR ...)
2) pick a connection (point to it)
2.1) If it is input/output: (by one click) build it. Done, don't carry on to step (3).
2.2) If it is ground: based on the icon in the bottom left corner, (after one click) place ghost of an unerected pillar or one stackable on the ground. Carry on to step (3).
2.3) If it is stackable: same as (2.2), but (after one click) don't place the ghost of stackable, the selected stackable might be the height the player desires. Carry on to step (3).
3) Choose the height of erection of pillar/stackable the same way the current pillars are built. So point as high as you want it.
Pillars: Can be built in the same heights as they are now. So 0, 1, 2 or 3 I believe.
Stackable: if building on a stackable, no stackables is the lowest option. If building on the ground, one stackable is the lowest option. You can build up to the max height of the world. But all is possible only if BIS.
4) Build: (one click) to build the desired belt and all the stackables/the pillar