Hei Astrid!
Korjaus:
Minun täytyy tunnustaa, että
olen ollut vasta
yhden kerran saunassa.
Se oli
(Saksassa,*) kun olin nuori, ehkä 16
vuotta**, (Saksassa). Valitettavasti siksi minulla ei ole tarinoita saunasta, koska
en muista hyvin.*** Luulen, että puusauna on parempi. Toivon, että
tulen/pääsen**** joskus Suomeen ja sitten käyn varmasti puusaunassa.
*It's better to put the place where you did it here, after telling that "it was (in Germany)", because that way you continue the sentence instead of telling the things seperately and it sounds better.
***You get the idea from that, but if you want to be even more clear, you can say it like for example "en muista sitä enää hyvin", = I don't remember it well anymore", because if you say it like "en muista hyvin", for example in some other sentence or even in this sentence, the listener can accidentally get the idea that you're bad to remember things (for example because you're sick or old).
**** If you talk to a person who already is in the place you want to go, it's better to say "I hope that
I come/'am able to come someday to..." instead of going. menen = I go, tulen = I come, pääsen (tulemaan) = I'm able to get/come.
**Just that you know, you can also say this like; 16-vuotias, or 16 vuotta vanha. In this case either of them would probably be better than just "16 vuotta", but in spoken Finnish that would be alright.
There always comes streak between the number and the word "vuotta(vuosi) = year" when the word "vuotta" is inflected. It's the same when talking about centuries etc. example;
the 20th century = 1900-luku,
in the 20th century = 1900-luvulla,
the 20th century's = 1900-luvun,
to the 20th century = 1900-luvulle...
You can compare:
17 vuotta =17 years
378 vuotta sitten = 378 years ago
68-vuotias = 68 years old
ennen vuotta 1398 = before year 1398
se on 10 000 vuotta vanha = it's 10 000 years old
The same with names:
En tunne Onni -nimistä henkilöä. = I don't know the person called Onni.
Se on Saara -nimisen tytön. = It's (the property) of a girl called Saara.
Kikka niminen tyttö. = a girl called Kikka.
There's actually three rules about the strikes, which have been taught to us at school, but to use them, you've to first know which words are compounded words and which aren't.
I did speak before about the compounded words, but I forgot to say that actually the first words (kivi) in the word, always explains the main word (talo) a bit like adjectives.
kivi=stone; explains the main word; it's made of stone, it's kivinen = stony
talo=house; main word
kivitalo= a house which is made of stone
The three rules;
The strike comes;
1. if the compounded word's explaning word (tuote = a product) ends to the same vowel, from which the main word (esittely = introduction) starts: tuote-esittely = an introduction of a product(s)
2. if one word of the compounded word is proper noun, character, number or foreign word: Jutta-täti = aunt called Jutta, A-luokka = class A, !5-vuotias = 15 years old, aerobic-tossut = aerobic-sneakers.
3. if one part of the compounded word has sanaliitto = "phrase".
Sanaliitto means that the word which would otherwise be writed as a compounded word, is instead writed seperately. Sanaliitto is quite complicated thing, but usually when the compounded word tells just a one thing, sanaliitto can include many different things. Usually the names of the books which includes two words, are "phrases".
Sanaliitto: Sinuhe, egyptiläinen -romaani. = Romany called Sinuhe, Egyptian.
One more thing:
I don't know is this same thing with the other languages, but you've maybe noticed that I use often this kind of part of sentences
"tieto- ja fantasiakirja = an instructional book and a fantasy book".
That comes when you use in the same sentence one after another two different compounded words, which have same ending word.
Then you don't have to write the later word twice.
No sentään yhden kerran.
Olen varma että pääset tänne vielä joku päivä, tai ainakaan se ei ole kielitaidosta kiinni. Kirjoitat jo erittäin hyvää suomea.
Minäkin olen sitä mieltä, että puusauna on parempi. Ilma ja sen tuoksu, sekä tunnelma ovat aivan erilaisia verrattaessa puu- ja sähkösaunoja.
Well, atleast once.

I'm sure you can get here someday, or atleast in the case you wouldn't get here, it wouldn't be because of your language skills. You write extraordinarily good Finnish.
I also think that wooden sauna is better. The air, it's scent and the atmosphere are totally different when compareing wooden saunas and electrical saunas.
Toinen teksti:
Viime viikolla olin työssä puutarhassa. Aurinko paistoi melkein joka iltapäivä, mutta ei ollut lämmintä. Se oli ensimmäinen aurinkoinen päivä huhtikuussa.
_* Leikkasin ruohoa ja istutin
pienen puun. Se oli kaunis pitkän talven jälkeen.
Talvella** meillä oli liian paljon
sadetta ja lunta.***
Nyt olen iloinen että kevät vihdoin
alkaa.****
* "Mä" is spoken Finnish and so I took it off, because all the other text is in formal Finnish, but as said before, you could use it when talking.

Anyways, in formal Finnish it sounds a bit repeating if you put the word "I" there, because people understands it already from the word "leikkasin (leikata)".
**I put "in winter = talvella" there, because otherwise you don't tell when or where was too much rain and snow and then you could speak about any time or place in the past.
***In this case the rain can also be plural "sateita = rains" (and here it'd be better like that), but the snow must be in singular form; "lunta", not "lumia". Actually the word "lumia" is extremely unusual, atleast what I think...
****Very usual way to say "The Spring starts or The Spring comes or came", is to say; Kevät koittaa (comes or starts in the future) , Kevät koitti (came). But grammatically that wasn't wrong.
Sorry that here's so much things writed red in the text, but I just thought you'd be easier to find things from it if reading later...
-Aurora-