I'm going to move a couple of the buttons in more toward the centre of the roof, just so it will be more secure - it's gaping a little at the front and that annoys me.
Elastic - I used hat elastic and if you choose to use elastic then don't use this as it's a little stiff and brittle. Go for hair elastics instead I think.
If you use elastic make sure the loops are being placed so they are positioned to secure the front of the house, not so that they are on the back walls - which are sewn in place and don't need buttons.
Seriously though - how bad is that baby's hair!
I thought if I wanted to I could always do more external detail later - but the internal detail was best done before sewing it all up.
Thread - One of the last things you do is put the wall structure (the supports) into the fabric and then sew it closed and I did this using invisible thread.
This way, the line that runs straight through the middle of my pond was not made too obvious.