I know this thread is closed but I'd like to bring up the suggestion again about the mesh sides that jeanm1963 mentioned before.
Yes, they can stick their heads out the top but...and let me speak from mid life experience here
...if your body gets hot just cooling off your head doesn't always help. If I get hot when I sleep and my head is already out of the covers I still need to kick the covers off to get cooled down...it would be the same for a dog in a carrier. If you could use the mesh and roll up sides it would allow air to flow through the entire carrier and the dog could get more comfortable when it needed to.
And let me say also...your carrier is very cute and it looks like you did a wonderful job making it.