بسم الله الرحمن الرحيم
If the Sherwani is not made of silk and no silver or gold thread is used to prepare it then it is lawful to wear it. You may wear it and may also wear it on the occasion of marriage. However, it is not lawful to wear it with extravagance and pride. However, according to Shariah, it is not good to wear such sophisticated and precious clothes. If gold or silver thread is used in the Sherwani then explain its quantity and submit the question again.
عن ابن عباس رضى الله عنهما قال: كل ما شئت والبس ماشئت ما أخطائتك اثنتان: سرف أو مخيلة رواه البخاري (2/ 860)
Allah knows Best!
Darul Uloom Deoband