I signed a contract with a home builder last year and gave the builder a deposit. Am I able to claim a financial loss because the builder filed for bankruptcy?

Unfortunately, no. This would be considered a personal expense, depending on the situation, a theft loss, however, theft losses are no longer deductible under the new tax laws. 

"Personal casualty and theft losses of an individual, sustained in a tax year beginning after 2017, are deductible only to the extent they’re attributable to a federally declared disaster."https://www.irs.gov/pub/irs-pdf/p547.pdf