I've written an article that covers writing a basic Custom Editor using C#

See: Using Custom Editors in Unity - C# example

Example from the article:

// MyScriptEditor.cs
using UnityEditor;

[CustomEditor(typeof(MyScript))] 
public class MyScriptEditor : Editor {

    public override void OnInspectorGUI() {
        MyScript myTarget = (MyScript) target;
        myTarget.MyValue = EditorGUILayout.IntSlider("Val-you", myTarget.MyValue, 1, 10);
    }
}

http://answers.unity3d.com/questions/11680/how-can-i-make-a-custom-inspector-for-this-object.html

I did just find a decent example..but looking more for a tutorial http://buchhofer.com/2011/05/scriptable-objects-and-custom-editors/