You need to start by understanding your needs. What are you going to use the power for? Is this a year-round or seasonal application? What is your climate like? Are your rooftops structurally suitable and do they face the equator? If not, what land is available, what direction does it face, and is it shade-free? Do you also have other sources of electricity; if so, what are they? Do you plan to keep/expand/get rid of them? Will your PV installation be tied into a larger electrical system (and/or the grid) or provide standalone power for specific loads? How much power will you need, and how will your usage be distributed throughout the day/year? Are permits and/or inspections required where you live? If so, which parts will you DIY vs. hire out, and what research, supplies, tools, and materials will be required to do the work in a way that will pass inspection?

Once you have some answers there, you can start figuring out what kind of equipment could meet your needs and pricing it out. "I want solar!" is not a constructive way to look at anything; it's a great way to waste a bunch of money on something that will end up not giving you what you want/need. Asking here is not the way to get this done; realistically you have at least several dozen hours of research ahead of you, much more if you are off-grid or really want to do every piece of the work yourself.

No particular tips on how to do it; but at least make sure you don't put too many in serial if you're at all concerned about fire safety.

My father was once involved in a big lawsuit over fires caused by faulty junction boxes and he swore he'd never let the total wattage exceed say 500, max 800, or so watts for panels installed on a house.

After all; it only takes a single slightly faulty contact and you essentially have an improvised arc welder on the top of your roof.

More generally, you need to be aware of the ratings and proper installation methods for the equipment and materials you are using. Nearly all PV modules today are rated for a 600V system voltage, as are most combiner boxes and common wire types. Not all breakers are, though! Higher voltage requires higher-rated and sometimes more expensive equipment as well as more careful work, but it allows longer wire runs with less copper which saves money, and it may enable you to use more efficient equipment as well. All depends on what you're trying to accomplish. If you aren't comfortable doing a 600V (or 300V, or 150V) wiring job, you need to weigh the disadvantages of lower system voltages (less flexible, more costly to wire, limited options for batteries and other equipment) against the cost of hiring someone qualified to do the work.

I don't subscribe to the idea that a rooftop system should be limited to 800W. An 800W system is not viable for grid-tied use (with modern modules you're looking at 3 modules in series which will not even give you 120V much less the required 340 or 480 to do proper grid-tied installation), and will not be cost-effective for an off-grid application unless you have a very small house, minimal power needs, and have a sunny climate year-round.

Know your needs. Know your abilities. Know your equipment. Safety first should not be in conflict with building a cost-effective system that meets your needs; if you can't figure out how to do so properly, hire someone who knows!

I'm not that up to date on the whole solar thing but I guess he then probably recommended not exceeding 600V (not W) for private uses.

The lawsuits were over high end equipment with higher ratings (I'm guessing voltage-wise) that had a small possible weakness which, when combined with installation which was too rough, ended up causing fires in hay-barns all over France.