Rainbow Dash checked the calendar on the wall again, making sure that today is really the day. How long has she calculated all the events? How long she has been waiting for the perfect time? Even she can't tell. This dream, after all, started even earlier than her wanting to be a Wonderbolt and had ever since kept this one to herself. It's something she wants to do herself.
Flying out of her house, Rainbow Dash looks up to the sky. It's sunny, yet it's not that warm. The weather forecast said it's going to be a little bit cloudy, so there's plenty of clouds that she can take without really messing up the weather. Increasing her altitude, the mare gently takes some normal sized clouds with both of her hooves, carefully gathering them in one spot just outside of Ponyville. She repeats the process around four times, and starts molding them into a bigger one. Her experience in the weather team really helped her.
Once she's done, the pegasus starts to inspect her creation, flying slightly above it. Hmm, no, not big enough. Rainbow immediately looks in the direction of the Everfree forest, one of the places where the weather isn't being controlled. Sure enough, she finds more clouds, including a big one. It's a bit dark, but she'll just have to drain the water a bit to purify its color into the usual white. Carefully using both hooves, Rainbow managed to pull the big cloud into her pile.
The pegasus steps on the combined fluff of clouds to drain any excess water until eventually, they all turn white. Then, using her hooves, she turns it into a shape similar to a boat. Building clouds into something isn't so different from building something with snow, and that's something Rainbow has experience with as well.
Confident that the shape is sturdy enough, Rainbow makes her way to Sweet Apple Acres. She had helped Applejack to bring some nice periodic rain over her place this last few months, making the grass fresh and able to provide food for her cattle. As a result, she'll have some extra bales of hay on the barn. The pegasus already asked before, and Applejack doesn't mind if she wants to take some, even though she thinks it's a weird form of reward for the pegasus after helping her.
Rainbow did just that, taking a modest amount of hay. It's not much, but it should be enough. Besides, though a mare with above average physical strength, Rainbow prefers not to carry luggage that's too heavy to be taken to the air. She's a Wonderbolt, not a mailmare. When she reaches the cloud she had gathered, she spreads the hay evenly on it, the pegasus making it comfy. Sure, clouds are fluffy and soft to lay on, but when you're born a pegasus, it's practically something you lay on during your entire life. It's time to make it a bit more... exotic. Heh, if she said something like that to Rarity, she'll definitely wail in anguish.
Speaking of Rarity, the pegasus remembers that she's supposed to take out any supplies in her boutique that she no longer needs, as the unicorn is going to try to make Manehatten her center of business. That means Rainbow is free to get some, even though no one would ever expect Rainbow to be near anything related to fashion. Her choice is seven rolls of ribbons, all in different colors. One by one, she drapes the ribbons on the cloud she had constructed in order of the color of the rainbow.
Her own personal space is looking good already, but she wants something else. Though a pegasus, Rainbow kinda wanted a treehouse when she was younger. The idea of one just looks cool to her, a small, secretive, and comfy house snug in the middle of branches and leaves. She thought about it, and maybe there's a way to make her little cloud reassemble a nice treehouse... sorta.
The answer lies behind her house. Thankfully, Twilight wasn't suspicious when Rainbow borrowed some books for gardening, even though she claims the knowledge was to help her parents. She had been growing some bushes there, and it's time to 'harvest' them. Carrying the plant, she carefully puts it all around the cloud, some of them slightly acting as a low wall to give her a bit more privacy. It's the trickiest part, but Rainbow Dash eventually got pretty satisfied with the end result.
Her next quest leads to Ponyville, where she knows the school is having arts and crafts day. Just like her previous friends, a certain Scootaloo is also supposed to help Rainbow, the mare already asking her to make some paper windmills. Only eager to comply because Rainbow previously helped the young filly into a Wonderbolt show, Scootaloo waits just outside the school to do the transaction, handing one of the windmills to Rainbow. Grateful for her help, Rainbow soon returns to her cloud, gently putting the windmill on it like one would put an ornament on a snowpony. As the gentlest breeze causes the paper ornament to turn, Rainbow almost squeed in excitement.
There are only two more things left, and they're both located in her house. The pegasus is quick to locate both, one is her Daring Do plushie, in particular the first thing she had ever bought from a con, and something she always treasure. The second one is a simple blue, triangular flag bearing the same symbol as her cutie mark. Pretty sure her parents gave it to her long ago, but she can't remember what for. The two mementos would be perfect for her cloud, and she quickly place them there.
Now, everything is ready. Rainbow finally has her own personal cloud, all for herself. The uniquely bushy cloud with streaks of rainbow colored ribbons on it looks so cozy, and exactly like the image her head projected all those years ago. Her Daring Do plushie has its back resting against the side, while both the flag and the windmill continue to interact with the wind. Pleased with her creation, Rainbow stands in the middle of the cloud, before laying down and closing her eyes.
She can picture it. Other ponies will ask her:
"This is your dream? Isn't this a bit childish?"
Maybe it is, but Rainbow believes that everypony has this hidden desire for a small, private place for themselves. Didn't everypony build a pillow fort once in their lifetime? Or hide under a blanket because it's cozy? So many foals want a treehouse or anything that can be called their 'secret clubhouse' or the like. Maybe even a small secret cave? A secret room in their house?
For Rainbow, her own big cloud to relax on is her version of that dream. It has been in her head since she attended flight school. After making sure all her ducks are in line, she finally makes that a reality, years in the making. All the hard work helping her friends, paying attention to the perfect weather, and a gap in her wonderbolt schedules finally pays off and fell today, the perfect day, more so because one of her lifelong dreams has been accomplished. The amount of satisfaction after all that is second to none.
Laying her head down on the soft hay covered cloud, Rainbow let out a relaxed sigh, and take a nice deserving nap.