There is always the parameters on the right hand side when you create an object.
If you have already created it, chenge it to an editable mesh, select the vertecies/edges/polygons you wish to move, and instead of using the gizmo and moving it freehand, enter its exact co-ordinates on the bottom bar.
after choosing an object to create, look on the right and look for "Keyboard Entry". you define the location to create and the dimensions and then click create and it appears.
After you create and before you turn to editabel mesh you can go to the Modifiers panel and continue to refine the dimentions so its just right and you can also change the segments for each dimension before you change to an editable mesh.
RenX question
