(I am not sure why the question got so down-voted, I'll try my best at least to answer.)
It was narrated that 'Umar bin Khattab said: "I heard the Messenger of Allah say: 'Whoever builds a mosque in which the Name of Allah is mentioned, Allah will build a house for him in Paradise.'" -- Sunan Ibn Majah 735 [grade: sahih] (sunnah.com)
The apparent meaning of the hadith you quoted is as you know and some mentioned, speaking about building a real world mosque, where people come to worship God.
But does that mean that you won't get a reward, building a symbolic mosque in a game for instance? So to your question: Is there a reward for building a mosque in Minecraft?
Of course it would depend on your intention as other mentioned. (Even building a real mosque would depend on the intention).
I would argue, that yes, you will get a reward from God building the mosque.
There is the famous hadith, related to Husn-Dhann (حسن الظن بالله) believing the best of Allah:
قَالَ اللَّهُ أَنَا عِنْدَ ظَنِّ عَبْدِي بِي
Allah's Messenger (ﷺ) said, "Allah said, 'I am to my slave as he thinks of Me, (i.e. I am able to do for him what he thinks I can do for him) (Sahih Bukhari - sunnah.com)
This has been interpreted that a person, according to how the person thinks of God, he/she might get that response. See for instance this article in arabic.
So, if a person having the intention of building the mosque in a game, which somehow might make other muslims playing the game, remember his religion and duties, why wouldn't you get rewarded? Even non muslims might become fascinated, maybe that is their first seed in spiritual growth leading the person to become a muslim.
So whoever does an atom's weight of good will see it,
Surat Az-Zalzalah, verse 7
We belive in God, being the most gracious, the One Who gives as much as he wishes.
With the statements above, yes, there is a reward for that. Only God knows how big the reward would be. And if he pleases, a house might be built for one in Paradise, even though its not a real life mosque (especially if we consider the hadith: I am able to do for him what he thinks I can do for him).
يُنفِقُ كَيْفَ يَشَاءُ
He spends (of His Bounty) as He wills