\documentclass{article}
\newcounter{myenumi}
\renewcommand{\themyenumi}{(\roman{myenumi})}
\newenvironment{myenumerate}{%
% stuff for beginning of environment goes here
\setlength{\parindent}{0pt}% don't indent paragraphs
\setcounter{myenumi}{0}% restart numbering
\bigskip% skip a line
\renewcommand{\item}{% new definition of item
\par% start a new line
\refstepcounter{myenumi}% advance counter
\makebox[2.5em][l]{\themyenumi}% print counter to width of 3em, aligned to left
}% end of definition of item
}{% at end of environment
\par% start new paragraph
\bigskip% skip a line
\noindent% don't indent new paragraph
\ignorespacesafterend% ignore spaces after environment
}
\begin{document}
Here is some regular text, and I'm going to go on a bit just to see where it wraps and all that.
\begin{myenumerate}
\item Here is the first item which goes on a bit so we can see how it wraps, and it still needs to be longer.
\item Here is another item.
\item Here is yet another item.
\item And this item is going to be much much longer so we can see another example of one that wraps.
\end{myenumerate}
Here is some more regular text, and let's go on a bit here too, just in case it's important how that looks too.
\end{document}