This is the nightly sleeper for our 6yo (queen) and 4yo (twin) boys, but we have in-laws who visit from out of town frequently and we also wanted a place to allow them to be comfortable as couples.
To accomodate adult headroom on the queen, I raised the entire loft 7" (72" high) and to fit the queen beneath, I had to lengthen the loft rails by 9" (84" long). To fill the resulting gap, I just used some 39" scraps of 2x4 and 2x6 overlapped to create a 4x10 landing which actually ended up a cool addition since it gives the kids a spot lower than the mattress to make the transition from the ladder to the mattress. It also has given us adults a spot to sit off the mattress while comforting them to sleep when needed, so we don't end up waking them when we leave.
I based the height of the queen legs (made four of them) off the size of a standard storage tote, which was ~13". We can fit 12-16 totes of clothes or other random storage under the bed as a result. The queen frame was just a simple 64"x84" rectangle out of 2x6s with 7 2x4s used as crossbeams to hold the mattress.
Note on the mattresses - these 8" memory foam mattresses are just as comfortable as our expensive name brand king mattress, but MUCH cheaper!
Despite raising the loft, I kept the height of the stair platform the same, but just added a second 'ladder' rung to get up to the loft (refer back to the 4x10 landing spot on the loft). To keep with the using available storage space theme, instead of attaching the stairs permanently, I used 1"x4" hinges to that we could swing the stairs up and put 4 more storage totes under there. (However, we quickly found that the kids liked that area as a 'fort', so we've left it open for their use.)
In the picture, you'll note there are four treads/steps on the stairs because I thought to myself "little feet, little steps" would be better. I soon learned that the littles are more than capable of using adult sized steps while adults nearly killed themselves coming down the little feet, little steps. As such, I ended up removing one of the middle steps and moving the new singular middle to a spot between the other two. Much better, stay with 3 steps.
While the queen can stand alone, I still attached it to the 'legs' of the loft so that our rambunctious boys didn't 'sweep the leg' and bring the whole thing down on themselves while under it.