Contignatio supra primum tabulatum est.

Because supra here is a preposition, and it normally takes the accusative when it means above or over.

So:

• supra = above
• tabulatum = floor/story
• primum tabulatum = the first floor/story

The adjective primum is accusative singular neuter because it agrees with tabulatum, which is also accusative singular neuter.

If you are wondering why it is not primo tabulato, that would be a different case, and it would not fit the usual construction with supra here.

Contignatio is nominative singular, and it is the subject of the sentence.

A good clue is the verb est, which is third person singular: is. That tells you the subject is singular. In this sentence, contignatio is the noun in the nominative, so it is the thing that is above the first floor/story.

So the structure is:

• contignatio = subject
• supra primum tabulatum = prepositional phrase
• est = verb

Latin does not have articles like English the and a/an.

So a Latin noun like contignatio can mean:

• a ceiling / a floor structure
• the ceiling / the floor structure

Which one you choose in English depends on the context.

That is very normal in Latin. Learners often want to find a separate word for the, but there usually is not one.

Because Latin word order is much more flexible than English word order.

In English, we strongly expect:

• The ceiling is above the first floor.

In Latin, the verb often comes at the end, especially in simple statements. So:

• Contignatio supra primum tabulatum est.

is completely normal.

Latin uses endings much more than word order to show what each word is doing, so moving est to the end does not make the sentence unclear.

In this kind of sentence, yes: supra as a preposition commonly takes the accusative.

That is why you see:

• supra primum tabulatum

not:

• supra primo tabulato

Also, supra can sometimes function more like an adverb in other contexts, but here it is clearly a preposition introducing the phrase primum tabulatum.

Because primum agrees with tabulatum, not with contignatio.

In Latin, adjectives must agree with the noun they describe in:

• gender
• number
• case

Here:

• tabulatum is neuter singular accusative
• so primus, -a, -um becomes primum

Even though contignatio is feminine, that does not matter here, because primum is not describing contignatio. It is describing tabulatum.

Primum is an ordinal adjective meaning first.

It modifies tabulatum, so together they mean:

• the first floor
• the first story

depending on how the meaning has been translated for the learner.

This is the same basic idea as in English:

• first floor
• second floor
• third floor

Latin uses an adjective for these ordinals just as English does.

Yes. Because Latin is highly inflected, several word orders are possible without changing the basic meaning.

For example, these would still be understandable Latin:

• Supra primum tabulatum contignatio est.
• Contignatio est supra primum tabulatum.
• Primum tabulatum supra contignatio est.
  though this last one is less natural stylistically

The original order is a straightforward and natural one, especially with the verb at the end.

That depends on the vocabulary meaning you were given, but grammatically the word is functioning as a noun meaning a level or flooring/floor area of a building.

In English, translations can vary:

• floor
• story/storey
• sometimes something closer to platform or decking, depending on context

So the grammar point to focus on is not the exact architectural nuance, but that tabulatum is the object of supra, and primum describes it.

A very useful beginner breakdown is:

• Contignatio = the subject
• supra = above
• primum tabulatum = the first floor/story
• est = is

So the pattern is:

subject + prepositional phrase + verb

That is a good way to read many simple Latin sentences: first find the main verb, then the subject, then any prepositional phrases or other modifiers.