Tool for designing CNN architectures
Given the number of parameters and the number of options for each parameter, a graphical tool (aka, graphical user interface or GUI) is not very practical for CNNs. Most practitioners store and manipulate parameters in text form.

There are two graphical projects for TensorFlow. Playground which is an in-browser network that can be modified and run on sample datasets. TensorBoard which visualizes the computational graph and helps with debugging models.