jlug-example.tex

\documentclass{beamer}
%\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{fontspec}
\setmainfont{calibri.ttf}
%\usepackage{hyperref}

% +++ Load theme from subfolder +++
% thanks to 'Symbol 1'@SE:
% https://tex.stackexchange.com/questions/275600/beamer-themes-on-custom-folder/284157#284157
\makeatletter
\def\beamer@calltheme#1#2#3{%
	\def\beamer@themelist{#2}
	\@for\beamer@themename:=\beamer@themelist\do
	{\usepackage[{#1}]{\beamer@themelocation/#3\beamer@themename}}}

\def\usefolder#1{
	\def\beamer@themelocation{#1}
}
\def\beamer@themelocation{}

\usefolder{theme}
\usetheme{jlug}
% --- End: Complicated theme loading  ---


\title{There shall be no ugly slides}
\date[Conference '00]{0th Conference of Conference Titles}
\author[Shortname]{Full Name \texttt{mailto:your.email@re.ss}}

\begin{document}
https://tex.stackexchange.com/questions/146529/design-a-custom-beamer-theme-from-scratch
\begin{frame}
\titlepage

\end{frame}

\end{document}