We are designing some custom speckle schema objects for grasshopper that will be used as templates for capturing metadata of large structures e.g bridges, tunnels. They only need to capture metadata and not any geometrical/model data.
What you are describing is the development of a Speckle Kit. Only Grasshopper Connector currently supports the use of these kits. Kits | Speckle Docs. The default Kit is Objects.
If you have created a custom Kit, you should place this as a compiled MyCustomKitName.dll in <MyUser>\AppData\Roaming\Speckle\Kits\MyCustomKitName\
This should then automatically be populated in Speckle for Grasshopper.