Can You Write Allah's Names on Walls?
Question

What is the ruling on writing the beautiful Names of Allah on walls? The schools have found a solution to the problem of people writing rude words on the walls of the school, which is to write the beautiful Names of Allah on the walls. Is this permissible? May Allah reward you with good.
Praise be to Allah.Understanding the Sanctity of Allah’s Names
The beautiful names of Allah, may He be Exalted, are names by which He has called Himself and revealed them in His Book, and His Messenger (blessings and peace of Allah be upon him) taught them to his Ummah by way of acquainting them with their Creator, so that they might believe in the divine perfection and majesty to which these names refer, and so that they might praise Him by reciting these names, and call upon Him thereby at times of ease and of hardship, and so that they may learn them and believe in them, so that they will have an impact on their attitude and conduct, as Allah, may He be Exalted, says (interpretation of the meaning):
{And to Allah belong the best names, so invoke Him by them. And leave [the company of] those who practice deviation concerning His names. They will be recompensed for what they have been doing} [Al-A`raf 7:180].
Also, the Prophet (blessings and peace of Allah be upon him) said: “Allah has ninety-nine names, one hundred less one. Whoever learns them by heart will enter Paradise.” (Narrated by Al-Bukhari, 2736 and Muslim, 2677)
Rulings from Scholars on Wall Art with the Names of Allah
Hence it is obligatory to venerate and respect these names, and indeed to hold them in the highest esteem. That cannot be achieved by writing them on walls  which are likely to get dust and dirt on them, and some of the letters may disappear, thus changing the names, and some of the children may write other words next to them or underneath them that are contrary to the respect that is due to them.
In brief, writing them as a kind of worship is not permissible; rather it is a kind of introducing a religious innovation into the practice of Islam.
Writing the divine names to protect the cleanliness of the wall is an abhorrent action,  and it comes under the heading of seeking worldly aims by doing actions that pertain to the hereafter, let alone what this involves of showing disrespect towards the divine names.
So, what is required is to keep far away from such actions.
Ibn Al-Humam Al-Hanafi (may Allah have mercy on him) said: “It is disliked to write Quranic verses and the Names of Allah, may He be Exalted, on coins, weapons and walls.” (End quote from Fat-h Al-Qadir,  1/169)
Ad-Dardir Al-Maliki (may Allah have mercy on him) said: What appears to be the case is that engraving words [on graves] is disliked, even if it is Quran, and it could be prohibited, because it leads to the words being mistreated and disrespected, as they mentioned. Similar to that is engraving or writing Quranic verses and the Names of Allah on walls.” (End quote from Ash-Sharh Al-Kabir ma‘a Ad-Dasuqi, 1/425)
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said: With regard to writing verses of Quran on walls, whether in the mosques or elsewhere, it is an innovation; there is no report from the Companions to suggest that they used to write verses on the walls. Moreover, writing verses on walls is a kind of disrespect towards the words of Allah.” (End quote from Al-Liqa’ Al-Maftuh, 197/13)
In Fatawa Al-Lajnah Ad-Da’imah (4/58) it says:
It is not known that the Prophet (blessings and peace of Allah be upon him) ever wrote any surah or verse of the Quran, or any of the names of Allah, may He be Exalted, on plaques or plates to be hung on the walls or in passageways for the purpose of adornment or seeking blessings, or to be a means of reminding people and conveying the message, or by way of exhorting and teaching people. The Rightly Guided Caliphs and the rest of the Companions (may Allah be pleased with them) followed his teachings concerning that, and the imams of guidance among the righteous early generations, who the Prophet (blessings and peace of Allah be upon him) testified were the best of generations after him (may Allah be pleased with them), followed in their footsteps. Hence they did not write any words of Quran, authentic Prophetic hadiths or the beautiful names of Allah on plaques, plates or cloth, in order to hang them on the walls  for the purpose of decoration, reminder or reflection after Islam spread and its territory expanded, and Islamic culture became widespread throughout the land, and literacy became common and many, various ways of conveying the message became available. They did not do that, even though they had a greater understanding of Islam and its objectives, and were very keen to spread Islam and convey its message. If this were something that is prescribed in Islamic teachings, the Prophet (blessings and peace of Allah be upon him) would have told us about it and guided us to do it; he and his Companions would have done it, and the imams of guidance  would have done it after him (may Allah be pleased with them).
Based on that, writing any words of the Quran or Prophetic Hadiths, or the beautiful names of Allah, on plaques or plates and the like, to be hung up as decor or for the purpose of reminder or reflection, or to be used as trade goods for the purpose of earning profit and persuading people to buy them, so that they may be a means of making money, thus undermining the dignity of the Quran and the Hadiths  of the Prophet (blessings and peace of Allah be upon him) and detracting from the noble objectives that Islam promotes, is contrary to the teachings of the Messenger of Allah (blessings and peace of Allah be upon him) and the practice of the Companions and the leading scholars of the early generations (may Allah be pleased with them).
Furthermore, these things may be subjected to mishandling at some point, when they are moved from one house to another or from one place to another, and they may be carried or touched by one who is Junub (one in the state of ritual impurity caused by the discharge of semen or sexual intercourse) or menstruating. (End quote)
For more details, please see the following answers:
Ruling on putting the verses of the Holy Quran as a background on mobile phones, computers and the like
Ruling on hanging Surat Al-Ikhlas on the rear window of the car as a reminder
Selling posters and frames of Quranic verses
Is it permissible to have the dua of entering toilet on the door of the bathroom
And Allah knows best.