In the emerging maker movement, clinicians have long played an advisory role in the development of customized assistive technology (AT). Recently, there has been a growing interest in including clinicians as builders of Do-It-Yourself (DIY) AT. To identify the needs of clinicians-as-makers, we investigated the challenges that clinicians faced as they volunteered in an AT building project where they were the primary designers and builders of assistive mobility devices for children. Through observation and co-building of modified ride-on toy cars with clinicians, we found that the rapid pace of development and transient relationship between user and builder did not allow for a complete assessment of the child's mobility. Furthermore, clinicians struggled to actualize concepts borne out of their clinical intent due to a lack of engineering skill. This study highlights the need for tools that support clinicians-as-makers in the AT maker process and a new conceptualization of the role of DIY-AT maker programs within the AT provider ecosystem.