grammar - Overall syntax of this sentence

この部屋はシャワーだけでお風呂がないんですが。
=> "This apartment only has a shower but no bathtub"

This would be what I think this sentence says contentwise. I also think it could be a viable translation, but the way its expressed confuses me.

First, I'm not sure if I understood the overall syntax of the sentence correctly. It seems to me that 部屋 is the topic here, but I dont think that it's the subject of the following clause.

"Concerning the apartment, with the shower only there is no bath."

Second, I'm struggling with the connection of

シャワーだけで

and

お風呂がない

Since I assume that the sentence says that there is a shower, but no bathtub, attaching both nominal phrases (shower and bathtub) to the predicative ない gives me a headache.

And here, the third unclarity comes into play.

What is this で? Is it the particle I was assuming? If so, are there any phrases omitted as well? I just can't imagine how shower and bathtub shall be connected to ない, so there must be an omitted verbal phrase expressing the existence of shower. Its either that or maybe you can explain how japanese can express the existence of something with a verb that's actually stating the non-existence of something ^^

Answer

この部屋はシャワーだけだ makes sense at least in conversation. It means something like "This room is shower-only" by itself. この部屋はシャワーだ (literally "This room is a shower") sounds weird in isolation, but it still makes sense in the context where you're talking about which room is equipped with what. It's in the same vein English speakers occasionally say "I'm coffee" at a restaurant.

So it's simply the two sentences said together: この部屋はシャワーだけだ and この部屋はお風呂がない. This で is the te-form of the copula だ.

EDIT: Sentences like この部屋はシャワーだ and 私はコーヒーだ are sometimes called うなぎ文 ("eel sentence"). They may look illogical at first, but are not uncommon in topic-prominent languages like Japanese.