Every contractor I've worked with has taken 50% up front and 50% when the job is finished. This is normal. One thing I would recommend is you vet your contractor thoroughly--check reviews, make sure they have a legitimate website, testimonials etc...
Pennsylvania has strict criminal laws that apply to contractors who negotiate contracts and perform home improvement jobs. A conviction for home improvement fraud can impact your freedom and privilege to work as a contractor in the future.
As a general rule of thumb your contractor rate should be at least 50% more than you'd get for the same work as an employee.