I plan to build a bunk bed rather than buy, i want something like that, here is an example of bed -https://10restbest.com/best-loft-beds-for-adults-and-kids . I looked at a few and would be similar in price to buy but not built as well. I will be using 1 1/2" 11 guage square tubing and 3/4" 11 guage square tubing. Here is what I was quoted for steel

HSS 1-1/2 * 1-1/2 * 11ga @ 24' $36.72 a stk

HSS 3/4 * 3/4 * .120 @ 11ga @ 24' $18.24 a stk

and here is a sketch.