Learn Hardcore Swedish: Butiken utanför stationen är ganska liten men trevlig. - The shop outside the station is quite small but nice.

Swedish marks “the” by attaching a suffix to the noun. Butik is an en‑word, so its definite singular is butiken (= “the shop”). You use this because you’re referring to a specific, identifiable shop. If you wanted to introduce a new, non‑specific shop, you’d use en butik. A bare butik without an article is generally not used in this kind of sentence.

Do I need the separate article den before butiken (like Den butiken …)?

No, not here. You only add the separate definite article (den/det/de) when there’s an attributive adjective before the noun (so-called “double definiteness”):

Predicative adjectives (after the verb): Butiken … är liten. (no separate article)
Attributive adjectives (before the noun): Den lilla butiken … (article + adjective + noun with definite ending)

Note that Den butiken … can mean “that shop” (demonstrative), which slightly changes the meaning.

Is utanför stationen part of the subject, or does it act like a place adverbial?

In this sentence it’s a postmodifier inside the subject noun phrase: Butiken [utanför stationen] = “the shop [outside the station].” This identifies which shop you mean. You could also treat it as a place adverbial in a different sentence, e.g. Butiken är utanför stationen (“The shop is located outside the station”), which states location rather than using it to identify the shop.

Could I say Utanför stationen ligger butiken instead of … är …?

Yes. For locations of buildings/places, Swedish often uses ligga (“to lie/be situated”): Utanför stationen ligger butiken. Using är is still grammatical, but ligger often sounds more natural for fixed locations.

Why is there no comma before men?

Because men here connects two adjectives in the same clause (ganska liten men trevlig). In Swedish, you add a comma before men when it connects two independent clauses:

No comma (same clause): … är ganska liten men trevlig.
Comma (new clause): … är ganska liten, men den är trevlig.

Why aren’t the adjectives inflected with -a or -t here?

They’re predicative adjectives (after är), so they agree with the subject like this:

Common-gender singular (en-word): base form → Butiken är liten/trevlig.
Neuter singular (ett-word): add -t → Huset är litet/trevligt.
Plural: add -a (or irregular form) → Butikerna är små/trevliga.

Why is it liten and not lilla or små?

Liten is irregular. Quick overview:

Attributive, indefinite: en liten butik, ett litet hus
Attributive, definite: den lilla butiken, det lilla huset, de små butikerna
Predicative, singular: Butiken är liten, Huset är litet
Predicative, plural: Butikerna är små

How strong is ganska? Does it mean “very” or “a bit”?

Ganska means “fairly/quite” — a moderate degree. It’s stronger than lite (“a bit”) but weaker than väldigt/mycket (“very/very much”). Near-synonyms include rätt (så) and hyfsat. So ganska liten is “on the small side” without being tiny.

What does trevlig imply when describing a shop?

Trevlig means “pleasant/nice.” For a shop it suggests a friendly or welcoming atmosphere, helpful staff, or a nice feel — not necessarily fancy or cozy. For “cozy,” you might say mysig; for visually nice, fin; for simply “good,” bra.

Do I need to repeat är or add den before trevlig?

No. In one clause you can coordinate adjectives without repeating the verb: … är ganska liten men trevlig.

Repeating the verb is usually unnecessary: … är ganska liten men är trevlig (possible but not idiomatic).
If you start a new clause, add a subject and comma: … är ganska liten, men den är trevlig.

Why is it stationen (definite)? Could it be en station?

It’s definite because you’re referring to a specific, contextually known station (“the station”). Utanför en station would mean “outside a station” (some station, unspecified), which is possible but changes the meaning and is much less likely in a context like this.

Where does ganska go? Could I say … är liten ganska?

Place degree adverbs before the adjective they modify: är ganska liten. You can’t say är liten ganska. With the copula är, the pattern is: subject + är + degree adverb + adjective.

Is butik the only word for “shop,” or can I use affär?

Both are common:

Butik: neutral “shop/store,” sometimes with a boutique/retail nuance.
Affär: “shop” in everyday speech (e.g., grocery), but also “business/deal” in other contexts. In this sentence, either Butiken … or Affären … would work.