Transforming yourself is entirely possible and there are no especial restrictions on it compared to performing it on someone else, and yes, it makes sense (both fictionally and mechanically) for it to be slightly easier—though it's not nearly as much easier as you might hope. It's actually remarkably straightforward to work up a generic template for these kinds of self-biomancy rituals (although your Preparation will usually be custom to each circumstance), as Rick Neal has done in his Practical Grimoire article as the "Rite of Icarus" flight-granting ritual. Do read that article—it's where I finally figured out what I'm about to lay out below.
There's a marginalis on page 283 of Your Story on how to transform a person, yourself or another. Basically, you need shifts enough to kill someone before (mechanically) you get narrative control enough over them to say what happens when they're taken out, or (fictionally) you get enough magical mojo dumped on them to reform them enough to grant superpowers (or, alternatively, turn them into a frog).
Since you, as your own target, want this to work, just assume you accept Consequences straight away instead of assigning any shifts of "damage" to your stress tracks, and that you decline to attempt to resist, putting your resistance at Mediocre (+0). That means your base complexity for any Thaumaturgical ritual involving transforming yourself is a considerable 21 (or, if your GM has adjusting the value of Consequences, whatever the sum of them is, +1 shift to Take Out).
Now you have to work in the cost of the actual effect you're adding. As the marginalis says, either there's an Evocation effect with an obvious shift cost that you want to add, or it's a Refresh-costing ability that will require temporarily giving up Fate points equal to the Refresh cost of the ability. Since this is the latter, you don't have to add any complexity to the ritual for that (thank goodness!), you just need to make sure you have enough Fate points left over to pay for the effect at the end of the ritual. And these are normal Fate points, not Refresh—as the sidebar "Temporary Powers" (YS97) cited in the marginalis says*, these are spent like normal Fate points, and the power temporarily gained doesn't come out of your Refresh at all.
That leaves duration—the default is "a scene", about 15 minutes, so move up the time ladder (YS315) for the actual duration you want and increase the complexity 1 per step, or leave it at "15 minutes" and leave the complexity at 21.
For a worked example, see the Rite of Icarus ritual in the aforementioned Rick Neal article, How to Build Spells, or A Practical Grimoire: Magic in DFRPG, Part Five. But let's do your specific super-strength ritual here, cribbing from Rick's Rite of Icarus:
Shadow of Atlas
Type: Thaumaturgy, transformation
Duration: a few hours
Effect: When the ritual is complete the caster must spend 2 Fate points. They gain inhuman strength, as the Inhuman Strength supernatural power, for three hours (or sunset/sunrise, whichever comes first).
Variations: A related but more complex ritual (complexity 26) has a duration of a full day (ignoring sunrise and sunset). Another related ritual, Disciple of Atlas, grants strength as the Supernatural Strength supernatural power, and the end-of-ritual cost is instead 4 Fate points.
Note that those variations are different rituals; they're not "boosters" you can just add on to the same ritual even though mechanically that's how we can model them—they're fictionally different rituals, performed differently during your Preparation phase and the ritual-casting itself, though they may bear obvious (to a wizard) similarities to each other. You can have any number of variations though, with different complexities and even entirely different supernatural powers, not just the two I tacked onto the end there as samples.
* When you read that sidebar though, ignore the part about "owing" the GM some compels if you don't have enough Fate points. It may seem like a tempting way to get high-cost powers with a ritual, but it doesn't apply to temporary powers gained from rituals. That provision is there for when the plot temporarily grants you powers—if you're doing it to yourself with a spell, it's your own responsibility to make sure you have the Fate points needed to complete the ritual!