The construction with nikui is verb root+nikui (+desu to make it polite). Be careful because this construction can have an unintended meaning. Never use tabenikui for your wife's cooking, or minikui unless you intend to be insulting.
It's the same as if you're trying to say "I want to [verb]." There are three kinds of verbs that are conjugated slightly differently, but the pattern is pretty obvious:
[TABLE=full]
[TR]
[TD]dictionary/plain form (type)[/TD]
[TD]polite form[/TD]
[TD]want to do[/TD]
[TD]easy to do[/TD]
[TD]hard to do[/TD]
[/TR]
[TR]
[TD]食べる taberu (ichidan verb)[/TD]
[TD]tabemasu[/TD]
[TD]tabetai[/TD]
[TD]tabeyasui[/TD]
[TD]tabenikui ("hard to eat," but also means not good, like mazui. Use with caution!)[/TD]
[/TR]
[TR]
[TD]見る miru (ichidan verb)[/TD]
[TD]mimasu[/TD]
[TD]mitai[/TD]
[TD]miyasui[/TD]
[TD]minikui (though this is "hard to see," it actually means "hard to look at/ugly." use with caution!) If you want to say "I can't see something (well), use "mienai"[/TD]
[/TR]
[TR]
[TD]見つける mitsukeru (ichidan verb)[/TD]
[TD]mitsukemasu[/TD]
[TD]mitsuketai[/TD]
[TD]mitsukeyasui[/TD]
[TD]mitsukenikui - hard to find. Can mean something is rare, depending on the context[/TD]
[/TR]
[TR]
[TD]切る kiru (godan verb)[/TD]
[TD]kirimasu[/TD]
[TD]kiritai[/TD]
[TD]kiriyasui[/TD]
[TD]kirinikui - hard to cut[/TD]
[/TR]
[TR]
[TD]読む yomu (godan verb)[/TD]
[TD]yomimasu[/TD]
[TD]yomitai[/TD]
[TD]yomiyasui[/TD]
[TD]yominikui - hard to read (could mean the character isn't written well, or that you have trouble recognizing what it says)[/TD]
[/TR]
[TR]
[TD]書く kaku (godan verb)[/TD]
[TD]kakimasu[/TD]
[TD]kakitai[/TD]
[TD]kakiyasui[/TD]
[TD]kakinikui - hard to write[/TD]
[/TR]
[TR]
[TD]作る tsukuru (godan verb)[/TD]
[TD]tsukurimasu[/TD]
[TD]tsukuritai[/TD]
[TD]tsukuriyasui[/TD]
[TD]tsukurinikui - hard to make[/TD]
[/TR]
[TR]
[TD]する suru (irregular verb)[/TD]
[TD]shimasu[/TD]
[TD]shitai[/TD]
[TD]shiyasui[/TD]
[TD]shinikui - hard to do[/TD]
[/TR]
[/TABLE]
you can also なかなか before verb+nikui, to emphasize that it's not easily done, or not easy to do well. Listen to native speakers and try to imitate how they use this construction.
~nikui and ~yasui themselves are conjugated like i-adjectives, hence the +desu to make it a formal sentence.