Layout the code structure and solution design for implementation. Look at Arbitrum coding guidelines. Create dummy interfaces with the code

Implement Data Entities, Messaging Module

Implement Unit Tests for the module, Implement Inbox Module

Implement Bridging Module, Utilities along with unit tests

Development Guide, Reference Implementation with examples

Arbitrum C# SDK Completed

C# SDK open source repository Nuget Package

Arbitrum Dev Tooling on One and NOVA 2.0