My son wanted a big-boy bed, as his converted crib was basically falling apart. We were going to make a clone of some other loft beds we had, however the supply cost was prohibitively expensive. Shame, it would have been an easy build. My wife saw plans on ana-white which I looked at and agreed to build with some structure modifications, notably doubling up on the leg girth.
The plans called for long pocket screws to hold everything together, but I wasn’t buying what they were selling. I opted for 5″ lag bolts at the major intersections, and 3″ screws elsewhere (where I wasn’t going through the long end of the 2x4s. Everything else was pretty by the book. I used a ton of 1x4s to support the mattress, and it’ll support a good 300lbs up there (combined weight plus mattress). I initially made the short ladder at 45º, but corrected it to 60º when I felt I needed either an additional step or to change the angle.
A very rewarding project, about eight hours in total spent on it. About $130 in materials, simple 2x4s, 2x6s and 1x4s, lag bolts and screws.