Measure your mixing console and audio monitors. You will need a table at least as wide as your mixer plus the width of your audio monitors. Factor in additional space for a keyboard, notepads, computer mouse, and a place to put your coffee.
Measure the depth of the mixing console, and add the depth of a rack case. The rack case will not only house your rack gear, but will also support your video monitor at a height conducive to proper posture. Again factor in a few extra inches of clearance between the mixer and rack case for cables, pens and pencils, and other supplies.
Purchase a table based on the dimensions you measured above. The table should firmly support the combined weight of the equipment you will place on it (mixer, audio and video monitors, rack case, preamps, equalizers, and other equipment).
Purchase a 6 to 8-space, 19-inch rack case to house your rack gear and support your video monitor. Six to 8 spaces will provide the proper video monitor height, but if you do not use a video monitor you may choose a larger rack case.
Measure the base of your audio monitors, and buy foam pads or wedges of at least the width and depth of the monitors, and of at least 2-inch thickness. The pads will both raise the monitors to a proper listening height and angle, and decouple them from the desktop for more accurate monitoring.
Assemble your DIY recording studio desk by placing the rack case in the middle of the desk, aligned with the back edge (opposite your sitting position). Place the foam pads for the monitors on either side of the rack case, leaving 6 to 8 inches clearance on either side of the rack case. Place your mixer, centered, on the desk in front of the rack. Connect all electrical gear with switchable power strips for easy power-up/power-down.