A system for constructing a form for forming a concrete structure is disclosed herein. The system may include a number of extensible form panels. An extensible form panel may be constituted with a basis frame having a basis frame section and an extensible frame section extensible for a variable amount in at least one direction, along one axis. The frame sections may be configured to respectively accept and support basis and filler facings. The extensible frame section may include male/female endings. The system may also include a capping member with male and/or female endings. A form panel may include hinges, which may be swivelable, drive screws, and/or electronic motors. The system may further include a stub free to facilitate vertical coupling of form panels. In various embodiments, the parts may be formed with reusable material or materials.