I made this by making a cube, go to attribute editor, select the model name, face editor, delete the face on the top middle, make another cube, move it above the other cube, delete the face at the bottom of the new cube, select both cubes, go to mesh and then combine, go to modelling toolkit, target weld, select the vertices of the top cube, connect them to the bottom cube.
I made these stairs by making a flat cuboid, duplicate it, move it above it, hold shift and press d to make the staircase. Rotate it for a spiralling staircase.
I made a fence in Maya by extruding shapes:
Finished render:
I modelled a propellor engine in Maya by extruding shapes and pressing 3 to make the model smooth:
