well there is perfect perfect, and reasonable perfect.
if you have access to a welder, some square stock and a shop, let me know.
otherwise - the first box I built a long time back was simple 2x4 construction with HDPE on top.
it's really quite simple, you don't need our help, just use a little common sense. Make a box out of 2x4's that is structurally sound, put bracing across the top every 24" max, and remember to countersink your screws and predrill holes so you don't crack whatever you use for a topsheet. Like you said, there are many threads in this cult about box building, and many pictures. learn with experience and by example of others.
also, if you're looking for perfect perfect, and you don't have the necessary tools, you could always buy one if you have some money around.