I downloaded a house and installed the files in the tray folder as instructed. What I can't seem to figure out is where to find the house in game. I went into free build mode on an empty lot but cannot locate any option to place an entire house. I can only find rooms and pieces of a house. Can someone direct me please? Thank you.

You should be able to find it in your library, then select it and have the option to place it.

I think it's the library i'm not finding. I see the save to library option but not the library itself.

Update: I found a library in the gallery option but the house I put into the tray folder is not showing up anywhere there.

You need to go into the 'advanced settings' and check 'include custom content' in the library