One of the joys of solar heating (evacuated tubes) over its cousin PV solar, is the fact you only need Part P certification/skills to install. Potentially, you could work with a standard roofer, plumber, and electrician to get the job done.
If you install to garage, please be aware that longer distance between tank and array affects performance in less favorable months.
Brandon’s tool hire rent out tower scaffolding platforms very cheaply, so overcoming the height issue is within your reach.
Hope this helps.