How to make Oblivion mods
Before you start the actual creation process of an Oblivion mod, you will need certain tools. First off, you will need the Construction Set, which comes with the Steam and GOG release of the game (if you do not have the construction set, it can be downloaded here). We also recommend installing the Construction Set Extender, which greatly improves the stability of the tool.
If you plan on making/editing models for your mod, you will need Blender (version 2.49b is recommended for Oblivion).