Ця будівля вища, ніж наш будинок.

Because будівля is a feminine singular noun, and Ukrainian demonstratives must agree with the noun in gender, number, and case.

So for this:

• цей = masculine
• ця = feminine
• це = neuter
• ці = plural

That is why you get ця будівля.

A useful contrast:

• ця будівля = this building
• це будівля = this is a building or it is a building in some contexts

So ця is specifically the adjective form matching будівля.

Because вища is the comparative form of високий meaning high / tall.

The basic pattern here is:

• високий = high, tall
• вищий = higher, taller
• вища = feminine form of higher / taller

Since будівля is feminine, the comparative adjective also has to be feminine:

• вищий будинок = a taller house
• вища будівля = a taller building

In this sentence, вища agrees with будівля.

Yes, from a learner’s point of view, it is best treated as an irregular comparative that you should memorize.

The adjective високий forms its comparative as:

• вищий = masculine
• вища = feminine
• вище = neuter
• вищі = plural

So the stem changes from висок- to вищ-.

This is a normal historical pattern in Ukrainian, but for learners the important thing is simply:

• високий → вищий
• not високіший in standard usage here

Because in Ukrainian, the present tense of to be is usually omitted.

So:

• Ця будівля вища literally looks like This building taller
• but it naturally means This building is taller

The verb є can appear in some contexts, but in ordinary sentences like this, leaving it out is the normal and natural choice.

Ніж means than in comparisons.

So:

• вища, ніж наш будинок = taller/higher than our house

It introduces the second part of the comparison.

A very common alternative in Ukrainian is за:

• Ця будівля вища за наш будинок.

Both are natural. For learners, ніж is often easy to understand because it matches English than very closely.

Because in standard Ukrainian spelling, ніж in this kind of comparison is normally preceded by a comma.

So:

• Ця будівля вища, ніж наш будинок.

This is the standard written form.

English does not always use a comma in the same way, so this can feel unusual at first.

Because after ніж, this part is understood like a shortened clause:

• Ця будівля вища, ніж наш будинок [є].

In other words, it is really something like:

• This building is taller than our house is

Because of that, будинок stays in the nominative, and наш also stays nominative to agree with it:

• наш будинок

So this is not a possessive form or an object form here. It is basically the noun phrase of the omitted clause.

Because наш has to agree with будинок.

Here будинок is:

• masculine
• singular
• nominative

So the correct form is:

• наш будинок = our house

Compare:

• наша будівля = our building
• наше місто = our city
• наші будинки = our houses

They are related, but not identical.

• будівля = building in a general sense
• будинок = house, and sometimes building depending on context

So in this sentence:

• ця будівля = this building
• наш будинок = our house

If you were comparing two general buildings, you could also say something like:

• Ця будівля вища, ніж та будівля.

But using будинок here is completely natural if the second thing is specifically a house.

It is grammatically possible, but вища is the more natural and standard choice here.

So:

• вища = normal, simple comparative
• більш висока = analytic comparative, possible but less natural in this sentence

For високий, Ukrainian strongly prefers the simple comparative:

• Ця будівля вища, ніж наш будинок.

Learners should usually use вища here.

No, Ukrainian word order is fairly flexible, but this version is the most neutral and natural:

• Ця будівля вища, ніж наш будинок.

If you change the order, the meaning usually stays the same, but the emphasis changes. For example, other orders may sound more literary, marked, or contrastive.

So as a learner, this sentence order is the safest one to use first.