I'd like to know how to correctly write a word "tabannusi" (build) in sumerian alphabet. Is there a chance then anyone can help me?
As noted by Draconis, this is not a Sumerian but an Akkadian word, specifically a form of the verb banû, "to build".
Specifically, I would analyze it as the G-durative (for the D-stem, the 2nd person prefix should be tu- instead of ta-) with a subjunctive marker -u- and an enclitic second person feminine object pronoun -ši,1 i.e. as tabanni+u+ši → tabannûši = "you (male2) will build (or are building) her/it (referring to a female person or to a grammatically female noun)". And, since the û is overlong (arising from a contracted diphtong) I would diverge slightly from Draconis's suggestion and spell it plene, i.e. as ta-ba-an-nu-ú-ši = 𒋫𒁀𒀭𒉡𒌑𒅆.3
In fact, I googled for the word and found that it occurs with that exact spelling in the Tale of Atra-ḫasīs, tablet III (which features the mesopotamian flood myth, and which was also substantially copied into the Epic of Gilgameš as tablet XI) on line 25, where the god Enlil is instructing Atra-ḫasīs to construct a boat to survive the coming flood:
- [e]-le-ep-pu ša ta-ba-an-nu-⸢ú⸣-[ši]4 = "the boat that you will build"
And yes, the conjunction ša = "that, which" indeed introduces a subjunctive clause here, and the word eleppu = "ship, boat" is grammatically female in Akkadian, explaining the suffixes.
Anyway, you can enter the transliterated spelling ta-ba-an-nu-ú-ši into a tool such as Cuneify Plus to get it spelled out for you in a cuneiform font of your choice. For example, in the Monumental Old Babylonian font SantakkuM (which I feel has a nice balance of artistic style and legibility), it looks like this:
1) Yes, the OP spells it with an s instead of š, but I'm willing to ascribe that to a minor misspelling and/or a legitimate spelling variation. In any case, there's no real ambiguity there, as -si does not occur as a distinct suffix in Akkadian.
2) If the subject were female, the feminine 2nd person verbal suffix -ī would override the subjunctive marker, and one would thus expect tabannī+ø+ši → tabannīši.
3) There are multiple signs in Akkadian cuneiform with the syllabic value /u/. Of these, u (a.k.a. u1) = 𒌋 is only used syllabically in late texts (its more common use is as the logogram for the number 10) while ù (or u3) = 𒅇 is normally only used to spell the conjunctions u = "and" and ū = "or". In all other words, the sign ú (or u2) = 𒌑 is by far the most common syllabic sign for this sound.
4) The full and half square brackets indicate missing and partial signs in the source text, typically due to the tablets having been damaged. While partially damaged signs are often still readable in context, fully missing signs must be reconstructed either based on lexical or grammatical grounds or by comparison with other sources featuring the same or similar texts. While I can't confirm this based on just the search results I found, I suspect the "[ši]" here was reconstructed by comparison with other editions of the tale of Atra-ḫasīs and/or with the Epic of Gilgameš.
This is an Akkadian word, a form of banû "to build". My grasp of Akkadian conjugation isn't the best, especially for "weak" verbs that lose one of their consonants, but it looks like a second singular feminine D-stem form: "you (female) are building". (Question for someone who's better at Akkadian: where's the S coming from?)
Since it's Akkadian rather than Sumerian, the spelling is relatively straightforward: ta-ba-an-nu-si. In Unicode that would be 𒋫𒁀𒀭𒉡𒋛 (generated with Cuneify). Choose a font appropriate for the time period you're interested in: in the "Assurbanipal" font (Neo-Assyrian), for example, it looks like this:
Cuneiform changed a lot over the millennia, so you can choose whichever form you like best; there are a variety of fonts available.