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...
Protect Yourself when Working with Custom Home Builders Only work with a licensed contractor. Get the contract in writing. Avoid “lump sum” bids. Talk to several contractors. Tie payments to deliverables. Get proof of payment to suppliers.