Ten budynek jest wyższy o dwa piętra niż nasz blok.

Because budynek is a masculine singular noun, and the demonstrative this must agree with it in gender, number, and case.

• ten budynek = this building
• to is used with neuter nouns, or as a general pronoun meaning this/it

Compare:

• ten dom = this house
• ta szkoła = this school
• to okno = this window

So budynek is masculine, which is why you need ten.

Budynek means building in a general sense.

Blok usually means an apartment block / block of flats / apartment building.

So in this sentence:

• Ten budynek = this building
• nasz blok = our apartment block

Using both words in one sentence is natural because one is a general word and the other is more specific.

Yes, in a normal sentence like this, jest is needed.

Polish often omits to be in some contexts, but not usually when you are describing something with an adjective in the present tense.

So:

• Ten budynek jest wyższy... = This building is taller/higher...
• Ten budynek wyższy... sounds incomplete or non-standard in ordinary speech

The adjective wyższy works here as part of the predicate, so jest is the normal form.

Wyższy is the comparative form of wysoki.

• wysoki = high / tall
• wyższy = higher / taller

This is not formed in a completely predictable way from the spelling of wysoki, so it is best learned as a set:

• wysoki
• wyższy
• najwyższy = highest / tallest

For buildings, wyższy is the natural word because you are comparing height.

Because the sentence is about height, not overall size.

• wyższy = taller / higher
• większy = bigger / larger

A building can be:

• wyższy if it has more height
• większy if it is larger overall

Since the sentence mentions two floors, it is specifically comparing height, so wyższy is the right choice.

After a comparative adjective, Polish often uses o + accusative to show by how much something differs.

So:

• wyższy o dwa piętra = higher/taller by two floors

This is a very common pattern:

• starszy o rok = older by a year
• krótszy o metr = shorter by a meter
• droższy o dziesięć złotych = more expensive by ten złoty

So in your sentence, o dwa piętra tells you the exact difference in height.

Because o in this pattern takes the accusative case, and with a non-masculine-personal noun like piętro, the form after dwa is:

• dwa piętra

Here:

• dwa = accusative/nominative form for two
• piętra = plural form used after 2, 3, 4

So:

• o dwa piętra = by two floors

You would see forms like dwóch in different grammatical environments, but not here.

Because after niż, Polish often keeps the compared noun phrase in the nominative, especially when the full meaning is something like:

• niż nasz blok [jest] = than our block [is]

So:

• niż nasz blok is correct and natural

By contrast, if you use od instead of niż, then you need the genitive:

• wyższy od naszego bloku = taller than our block

So both of these are possible in Polish:

• Ten budynek jest wyższy niż nasz blok.
• Ten budynek jest wyższy od naszego bloku.

But with niż, nasz blok is normal.

Yes, you often can, but the structure changes.

With niż:

• Ten budynek jest wyższy o dwa piętra niż nasz blok.

With od:

• Ten budynek jest wyższy od naszego bloku o dwa piętra.

Important difference:

• niż is followed here by nasz blok
• od requires the genitive, so it becomes naszego bloku

Both mean the same thing, but niż is the more direct equivalent of English than.

Because blok is a masculine noun, and nasz must agree with it.

Compare:

• nasz blok = our block
• nasza szkoła = our school
• nasze mieszkanie = our apartment

So the form depends on the gender of the noun:

• masculine: nasz
• feminine: nasza
• neuter: nasze

Yes. Polish word order is flexible, although some versions sound more neutral than others.

The original sentence is natural:

• Ten budynek jest wyższy o dwa piętra niż nasz blok.

You could also say:

• Ten budynek jest wyższy niż nasz blok o dwa piętra.
• Ten budynek jest o dwa piętra wyższy niż nasz blok.
• Ten budynek jest wyższy od naszego bloku o dwa piętra.

All of these are understandable, but the original version is clear and idiomatic.

Yes, if the context already makes it clear which building you mean.

• Budynek jest wyższy o dwa piętra niż nasz blok.

That means The building is two floors taller than our block or This building..., depending on context.

Keeping ten makes the sentence more specific and more like this building. It helps point out a particular building.