spawn and destroy with toggle button?

Are you using the newer, more-in-the-editor style of UI, or the older GUI.Toggle sort of stuff?

For the aesthetic (text and colour) component:

In the case of the newer style, you would need a reference to the Toggle script on the UI element and the relevant components (the Toggle GameObject's Toggle script for access to the ColorBlock where you can set the normalColor as necessary, the Toggle GameObject's child Label to set the text). The code for this would look something like:

 // toggle is the Toggle script from the Toggle GameObject
 // toggleText is the Text script from the Toggle's child Label
 
 public void ToggleCubeUIElement(bool currentValue) {
     if (currentValue) {
         // toggled to ON, prepare UI for turning OFF
         toggle.colors.normalColor = Color.red;
         toggleText.text = "destroy cube"

     } else {
         // toggled to OFF, prepare UI for turning ON
         toggle.colors.normalColor = Color.red;
         toggleText.text = "spawn cube"
     }
 }

You'll need to ask someone else for how to do it for the older style in terms of colourizing, but the principles are more-or-less the same (reacting to the state change).

For the functional component:

In both styles, you're addressing some change to a bool value and you'd do well to set up a method that simply takes the updated value (e.g. when the toggle is flipped). This also helps break up your code a little which may make management a bit easier.

From here, the method would look something along the lines of:

 // cubePrefab is a prefab or GameObject to create
 // cube (GameObject) is an instance of the cube
 // position is a Vector3 to create the cube at
 
 public void ToggleCube(bool currentValue) {
     if (currentValue) {
         // toggled to ON, spawn cube
         cube = (GameObject) Instantiate(cubePrefab, position, Quaternion.identity);

     } else {
         // toggled to OFF, destroy cube
         Destroy(cube);
     }
 }

My apologies if there are any code errors as this was written so far mostly off of the top of my head.

Is this what you were looking for?