My shape is the wrong size

Your shape is a speck, or it fills the screen and you cannot find the rest of your scene. Both come from the same thing: one unit is one metre, and it is easy to lose track of that once numbers are being multiplied together.

Work out what size it should be

A door is about two. A crate is about one. A person is about 1.8. A tree is five to fifteen. A whole scene wants to stay under about forty across.

If your number is far outside that, the app will say so rather than letting you find out later when the thing is in a game and dwarfs a building.

Very small is worse than very large

Too big is annoying. Too small is destructive, and it does not look like a size problem.

Welding, cutting and merging all compare real distances. Build at a hundredth of normal size and the detail you carefully added falls inside those distances, so it merges into itself and disappears. The shape comes out simpler than you built it and nothing errors.

Build at a sensible size and scale at the end if you need to.

A number that stopped moving

Every setting has a range, and a value beyond it is pulled back to the edge rather than refused. If a knob stops making a difference partway along, it has probably hit its limit and the extra is being discarded.

The shape is right but it sits wrong

Half below the floor is not a size problem. A shape is built around its own middle, so it needs seating. Place On with nothing wired into its Base moves a shape so its underside sits at zero, at whatever size it currently is.

Put it after anything that changes the size, not before. A Transform after the seating sets its own position and undoes the seat.