How Can I build a large led screen?
The MAX7219 is a driver for up to 8x8 LEDs. It needs a single-bit data input, a bit clock and a frame clock input. As that display module already has four 8x8 LED matrices, it most likely has 4 data inputs, a bit clock and a frame clock. So, 6 GPIOs. For each of those modules, you need another GPIO for a separate bit clock, and this will divide the possible frame rate of the screen by two. But as the MAX7219 supports up to 10Mbit/s data rate, it shouldn't be a problem to arrange numerous of those modules to one big screen.

EDIT: I have to correct myself, the MAX7219 also has a data output, so that module most likely needs only 3 GPIOS. And one should use the "frame clock" (LOAD input) to separate modules, not the bit clock.