You buy the land, appoint your own architect and contractor, and build to your own brief. Every build goes through Sharjah Municipality and SEWA before connection.
Check who can buy first. Most of these districts are restricted to UAE and GCC nationals, and Al-Hoshi to Arab nationals; Tilal City is the exception. Drive times are off-peak estimates: the Sharjah to Dubai run at 7am is a different journey entirely.
