DIY: Gallery Wall Arrangement Ideas - plus many other guides, such as yardage guides for upholstered furniture, window treatment & terminology guides, area rug size guides, etc. This is an excellent resource!!!
Spiral Gallery Wall Layout Tip: start with placing the center frame, and then spiral out the other frames in the arrangement you see. Make sure there is an even amount of space between all of the other frames and the center frame. The outer frames will lend to a natural square shape.
How To Create a Gallery Wall on a Budget - I was able to purchase IKEA Ribba frames in a variety of sizes for just under $200. My notes on the diagram above show the breakdown of sizes and associated costs. I bought 14 frames but used 13 for the collage. I decided to mix the wood and black and purchased half of each finish.