How to upload a house on PlatinumSimmers
Make sure you are logged into the site, then press the Downloads button at the top of the page.
You will get this window:
Press Upload File at the right/top
Then choose the Sims 3 > Lots > houses category
Upload the sims3pack, pictures and fill in the text.
If you are entering the competition make sure to use the tag "greenhouse" or let us know in the Description that its an entry.
When you are done press 'add submission'.