Laravel Homestead just received a new update with support for PHP 7 which is due out this month.
If you are already using the PHP 5.x Homestead box, you can upgrade your installation to PHP 7.0 by cloning the php-7 branch of the laravel/homestead repository into a new folder:
git clone -b php-7 https://github.com/laravel/homestead.git Homestead
Next add the box directive to the top of your existing Homestead.yaml file:
box: laravel/homestead-7
Finally, you can run the vagrant up command from the directory that contains your clone of the laravel/homestead repository.
For more information consult the official documenation and also checkout Laracasts PHP 7 video series.