Unity3D: how to add models dynamically at runtime in unity web output?

This might help you It turns out that the Drag and Angular Drag properties of the DragRigidbody script associated with each cube were overriding the same properties of each Rigidbody. The DragRigidbody script values were 10 and 5 for Drag and Angular Drag, respectively, and I just never noticed them before.
I still don't know why I wasn't having problems with only a single cube though. In any case, setting the values of the DragRigidbody script to the same as those in Rigidbody got things working.

Does that help Unity Asset Store TOS (Terms of Service):

it fixes the issue I highly advise you to instantiate a prefab instead of creating the button from scratch.
A gameobject with a RectTransform and button only won't be visible, and won't react to clicks, because you need additionnal components (such as Canvas Renderer and Image / Raw Image).

// Drag & Drop the prefab of the button you will instantiate
public GameObject buttonPrefab ;

public void MakeButton(string direction)
{
    // Instantiate (clone) the prefab    
    GameObject button = (GameObject) Instantiate( buttonPrefab ) ;

    var panel = GameObject.Find("CommandPanel");
    button.transform.position = panel.transform.position;
    button.GetComponent<RectTransform>().SetParent(panel.transform);
    button.GetComponent<RectTransform>().SetInsetAndSizeFromParentEdge(RectTransform.Edge.Left,0,10);
    button.layer = 5;

}

I wish this help you im building a city-builder game and i wanted to get your input on the best (performance wise) way to simulate a building being build. I have 5 .fbx models for different stages of the building progress (20%,40%,60%,80%,100% done). So my question is what is the best way to add these models in the game and change them out during the building progress. , It depends from situation to situation. Few cases:

should help you out Although I don't have direct answer to your question, let me comment on some details.
Using importlib would be the easiest choice I believe. Once you've imported such a generated module on the top of the file, it's clearly obvious wether you've loaded it successfully or not.