Why?

Welcome, if you are a no-nonsense, pun-intolerant kind of person, I recommend skipping ahead to paragraph 2. If you think raising your bed to 6 feet off the ground might be difficult or expensive, I'm here to debunk that notion. It's not as lofty of a goal as you might think. This project may be over your head, but it doesn't have to be out of your reach. Alright, with that out of my system, let's get into it.

I started making this bed (like the shoe rack: https://www.instructables.com/id/Simple-Cheap-Shoe...) in order to create the least expensive option possible to maximize space in very small apartment room. The good news is that despite the room being small (9'x10') I do have 9' ceilings, so I was able to build it with walking height underneath (6 feet), while still having 2 feet between the bed and ceiling.

Criteria:

Everyone's criteria for a project like this may be a bit different, so I will give you mine, and tell you how I came up them to hopefully help you work through that process yourself.

As previously mentioned, I wanted it at a height where I could walk under. Although I mostly sit at my desk when under it, I does take up half the room, so it would have been fairly frustrating for it to be only suited for sitting. I am just over 5'9", so I decided to place the bottom of the bed at 6'.
I had it in my head that I wanted a queen mattress, but I probably should have just gone with a full... hindsight, right? Once you know what size mattress you want, you can refer to the chart above for dimensions.
I wanted to make a pretty simple version because I didn't want to spend a lot. I already had the 2x4s, so I ended up spending about $160, which is more than I anticipated, but still a lot less than I could have bought one for.
The one place I did incur a little extra cost than I 'had to' was the stairs. I could have just done a basic ladder from 2x4s and save about $25. However, because the space was small and storage was limited, I decided to build stairs with built-in storage. The instructions for those will be at the end, so if that is not something you need, you can skip that step and save $25 as well as some time, and I will leave the creating of a ladder in your very capable hands.

Tools:

Here are the tools I used:

Jig saw
Drill
Phillips Driver Bit
3/8" Paddle Bit
Speed Square
Miter Saw
Impact Driver
Channel Locks

Materials:

Because I am leaving sizing open depending on your specific build, I will list the type of board, and how many you need for each part of the bed, then once you know what size you are building, you can determine the length of your cuts.

(2) 4'x8'x1/2" plywood
(2) 2"x6" for the length of your bed
(2) 2"x6" for the width of your bed
(4) 4"x4" posts
(5) 2"x4" the same width as your mattress
(1) 2"x4" the width of your mattess + 7" (floor brace)
(1)2"x4" the length of your mattress + 7" (side brace)
(8) 3/8" bolts
(8) 3/8" lock nuts
(8) 3/8" washers
(10) 2x4 mounting brackets
1/4" wood screws
3" wood screws

If you are building the stairs I will give you my dimensions since they are mostly unrelated to the mattress size. My stairs are 4' tall over the 5' width of the mattress with 4 steps. This makes each step is 18" wide and 15" deep with a 12" riser. You will see from the photos that I use 2x4s to build the stairs because it was easy and I had a bunch of old ones waiting to be used, but you could easily rip them into 2x2s with a table saw and they would be plenty sturdy for anyone up to my size (I weigh about 150lbs) and probably a bit bigger.

(1) 4'x8'x1/2" plywood (and the leftover from the bed)
(4) 2"x4"x4'
(2) 2"x4"x3'
(2) 2"x4"x2'
(2) 2"x4"x1'
(13) 2"x4"18"

Final Note: Since I was building this bed for my apartment I had no place here to work on it, so I had to do it at my parents house about an hour away. It was also too big to setup and then move in, so it had to be setup in the room. Because of that I had no chance to fix things once I got it setup. So, as you read through each step I will have added a Lessons Learned section to tell you the problems I have found and things I wish I would have done differently. I hope it is beneficial to you.

Step 1: Building: Posts & Supports

The posts, as listed in the materials, are 4x4 posts, while the frame around the top of the 4x4s is made from 2x6s. Let's look at the layout for the structure and hardware of these pieces.

I used 3/8" bolts with washers and lock nuts to secure the 2x6s to the 4x4 posts. At each corner the long 2x6 overlaps the short one (see diagram above). You want to put the bolts as close to the center of the joint as possible, but since doing this from both 2x6s into the 4x4 would cause them to collide in the middle, they have to be shifted. Since the joint overlap is 4" wide and 6" tall, I decided to shift the bolts up and down. I chose one and moved it up 1/4" and moved the other down 1/4" (as illustrated in the second diagram).

I measured and marked where the 2x6 would overlap the 4x4 and drilled through them while they were overlapping to ensure the holes would line up properly. It is always advisable to use a square during this process to produce accurate angles. Repeat this process on all four posts and you should have a fully supported, elevated border with inner dimensions the same as your mattress, plus a 4" gap at the head and foot between your posts. We will use the space at the head in a later instructable when constructing the headboard.

Lastly, I used some 2 1/2" screws to add some 2x4 braces. I put one across the back at about waist height, and one on the floor across the head end.

Lesson Learned: With no corner or X bracing, the bed is a bit wobbly, so that I something I am planning to go back and add.

Step 2: Building: Platform

Okay, I probably went a little overboard on the strength of the platform. I laid five 2x4s, on roughly 16" centers, across the width of the bed between the head and foot. I mounted them with joist hangers to the inside of the long 2x6s. I then cut the 1/2" plywood to fit on top of the joists inside the 2x6 frame. By aligning the 2x4s with the bottom edge of the 2x6s, the mattress sits about 2" deep in the frame

Lesson Learned: mount a 2x4 (oriented with the 4" horizontal) between the two posts at the head, then do the same for the two at the foot. Align the top of these to be flush with the top of the joists. This will give end support to the plywood. On the head end, it will also serve as some support in the next instructable when making the headboard. On the foot end, it creates a nice lip to use when climbing into the bed.

Step 3: Building: Stairs

So, you decided to make the stairs. Or maybe you're just reading through to see if you might want to, Well, here we are just going to look at how to make the basic stairs. In the follow up instructable we will turn them into storage.

The first thing I did was cut the stair shape out of the 1/2" plywood. As mention in the intro, these steps are 1' tall and 15" deep with 4 steps, for a total of 5' long and 4' tall. At the front edge of each step I created 2x4 rectangles the same height as the step. On the back of each step (which is the front the the next step I attached a cross member to support the back of the plywood that will go on top. After all of the triangles were created and atach to the plywood, I cut the pluwood erctanges for the top of the steps. These were 18" wide and 15" deep. That is basically it just to create a functional skeleton of the stairs.

Step 4: Conclusion

I definitely made some mistakes and learned some things during this build. First and foremost is that I should have taken the time to assemble everything at my parents house once it was cut, make adjustments, then disassemble it for transportation. Besides the bit of wobbliness, the bed has functioned very well and has been comfortable to sleep in. I have an 8" Gel foam mattress on it, and it is serving me well. Stay tuned for the follow up 'ible on adding shelving, lighting, and a headboard, as well as finishing out the stairs into a functional storage space. Happy Making!