\documentclass{beamer}
\usepackage[english]{babel}
%\usepackage[orientation=landscape,size=custom,width=16,height=9,scale=0.5,debug]{beamerposter}
\usepackage[orientation=portrait,size=a0,scale=1.25]{beamerposter}
\usepackage{fancybox} %ovalbox
\usepackage{framed}
\usepackage{lipsum}

%\usetheme{Antibes}
%\usetheme{Berlin}
%\usetheme{Rochester}
\usetheme{default}
\usecolortheme{beaver}

%%%%%%%%%
% title %
%%%%%%%%%
\setbeamertemplate{headline}{
\leavevmode
\begin{columns}
\begin{column}{\linewidth}
\vskip1cm
\centering
\usebeamercolor{title in headline}{\Huge{\textbf{\inserttitle}}\\[0.5ex]}
\usebeamercolor{author in headline}{\Large{\insertauthor}\\[1ex]}
\vskip1cm
\end{column}
\vspace{1cm}
\end{columns}
\vspace{0.5in}
\hspace{0.5in}\begin{beamercolorbox}[wd=47in,colsep=0.15cm]{cboxb}\end{beamercolorbox}
\vspace{0.1in}
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% rounded box around blocks %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\renewcommand\fbox[1]{\Ovalbox{#1}}
\renewcommand*\FrameCommand{\ovalbox}

\setbeamertemplate{block begin}{
\begin{framed}\vspace{1ex}\begin{center}\begin{minipage}{.98\textwidth}
\begin{beamercolorbox}[colsep*=0ex,dp={2ex}]{block title}
\usebeamerfont{block title}\large\insertblocktitle
\end{beamercolorbox}
{\parskip0pt\par}
\ifbeamercolorempty[bg]{block title}{}{\ifbeamercolorempty[bg]{block body}{}{\nointerlineskip\vskip-0.5pt}}
\usebeamerfont{block body}
\begin{beamercolorbox}[colsep*=0ex,vmode]{block body}
}

\setbeamertemplate{block end}{
\end{beamercolorbox}
\vspace{1ex}
\end{minipage}\end{center}\end{framed}
}


\title{Nice minimal working example}
\author{manu}

\begin{document}
\addtobeamertemplate{block end}{}{\vspace*{2ex}} % White space under blocks
\addtobeamertemplate{block alerted end}{}{\vspace*{2ex}} 

\begin{frame}{}

\vfill
\begin{block}{Foobar}
\lipsum[1]
\end{block}
\vfill

\begin{columns}[t]

\begin{column}{.48\linewidth}
\vfill
\begin{block}{Lorem}
\lipsum[2]
\end{block}
\vfill
\end{column}

\begin{column}{.48\linewidth}
\vfill
\begin{block}{Ipsum}
\lipsum[3]
\end{block}
\vfill
\end{column}

\end{columns}

\begin{columns}[c]

\begin{column}{.3\linewidth}
\vfill
\begin{block}{Dolor sit}
\lipsum[4]
\end{block}
\vfill
\begin{exampleblock}{Example}
\lipsum[4]
\begin{enumerate}
\item lorem
\item ipsum
\item dolor
\end{enumerate}
Justo vitae lacus tincidunt ultrices.
\end{exampleblock}
\vfill
\end{column}

\begin{column}{.3\linewidth}
\vfill
\begin{block}{Dolor sit}
\lipsum[5]
\begin{itemize}
\item $1^{\text{st}}$ item
\item second item, very important item
\item third item
\end{itemize}
\lipsum[6]
\end{block}
\vfill
\end{column}

\begin{column}{.3\linewidth}
\vfill
\begin{alertblock}{Alert}
\lipsum[7]
\end{alertblock}
\vfill
\begin{block}{Block}
\lipsum[8]
\end{block}
\vfill
\end{column}
\end{columns}

\end{frame}

%\begin{frame}{second frame}
%\begin{block}{Lorem}
%\lipsum[4-6]
%\end{block}
%\end{frame}
\end{document}
