Creating an Inscription does NOT require a previous transaction.
Here is what the header should look like when creating an inscription:
{
"action": "createbim",
"timestamp": number,
"data": {
}
}
Here is what the data field should look like:
"data": {
"bimData": "base-64 encoded data", // The actual data of the BIM
"sendTo": "address" // The address to send the BIM inscription to
}