Merkle root with one transaction

I am trying to build a merkle root which contains only the coinbase transaction from bitcoind

After creating the coinbase transaction i need to convert it to little endian, hash it twice and then put it in the blockheader as it is, or i must reconvert it again before i put it in the blockheader

I mean:

step 1: convert coinbase transaction to little endian

step 2 : double SHA256

step 3 : reconvert to little endian or let it as it's?

step 4 : put it on the blockheader

I am a little confused

Thank you for help