There are a lot of options out there when it comes to 3d printer build surfaces. Many people swear by bare borosilicate glass or mirrors. Other's add a layer of glue stick, hairspray or even salt water. Also, what should the build plate be made of? PCB heaters are fairly popular and even ship on some higher-end retail printers. So why bother with anything else? Well, let's get into that.
I do not recommend printing PETG on bare glass as it can bond permanently and damage or destroy your glass.
Unless you're using mic-6 tooling plate for your build plate, you're probably going to need to print on a piece of glass. Borosilicate glass is the most popular choice because it has excellent resistance to thermal shock. However, lots of folks claim to get similar performance from regular glass which is much cheaper than boro. Your mileage may vary.
PCB Heater + Borosilicate Glass
Most retail and kit 3d printers come with a PCB Heater with a piece of glass or some proprietary build surface. It's the quickest and cheapest way that technically kind of works. The problem with PCB Heaters is they're always over-constrained which means they warp or bend as they heat up. That, in turn, leads to air gaps between the heater and your borosilicate glass which then leads to temperature variations on your build surface. You can fill the gaps with silicone thermal pads and that's how I did it for a long time.
Another downside is most of them ship with four leveling points, which is bad. So if you want to upgrade to three leveling points, you're restricted by the holes the manufacturer put in the PCB. So you might not end up with an ideal configuration. If your printer came with a PCB heater and it's working fine for you, no problem. You do you. But if you're looking for upgrades, this is a good place to start.
Aluminum Sheet + Silicone Heater
This can be a good improvement on the above. You can buy ready-made build plate kits that include the carriage and build plate in just about any configuration you can think of. Once you have the kit, it's very easy to use some red RTV Silicone (I'm a fan of Permatex) to stick an inexpensive silicone heater to the bottom, clip a piece of boro to it and off you go. It's easy to modify if you want to change up your leveling system. Very much "middle-of-the-road" and maybe the best option if you don't have access to power tools for cutting and machining aluminum.
Often, on the other hand, the aluminum sheet will arrive warped. Even it's straight when you get it, it's very easy for a head crash to warp aluminum sheet. I found this out not long after I upgraded my first printer with an aluminum sheet kit when I was experimenting with a home-made z-probe. You know me, all ignorance and enthusiasm.
Mic-6 Aluminum + Silicone Heater
This is the best option, in my opinion. This is how you build a professional level build plate. It doesn't get any flatter than Mic-6 for a 3d printer build plate. It's expensive if you price it retail but you can buy remnants that are plenty large enough for a build plate on eBay for cheap. You can cut it with just a hacksaw if that's all you have available. However, a $20 jigsaw and some good blades work so much better. Clamp it down solidly but be careful not to deform the aluminum.
Some light machining (can be done with a hack/jigsaw and file if nothing else), stick a silicone heater to it and you've got the best build plate around. It's rigid and difficult to warp, though easy to "ding" so handle it gently. If you really want to go pro, stick a sheet of PEI on top of it and you've got the best build plate with the best print surface. Effective, efficient and low-maintenance. It's not much more expensive than a ready-made kit made from an aluminum sheet, though does require a DIY attitude. Well worth the work upfront for a headache it'll save you later.
print surface quick comparison
Clean with IPA for PLA
Clean with Windex for PETG
PETG will bond permanently
Leaves a smooth finish
glue stick/hair spray
Helps PLA stick
Release agent for PETG
Kind of messy
Hairspray must contain co-polymer
Clean with IPA to remove residue
Cheap, easy to replace
Makes up for slight variance in Z-height
Doesn't leave a good finish
Transfers heat well
Prevents PETG from damaging glass
Expensive, hard to find
Kapton narrower than build plate can be difficult to apply
Works great without any coating
Durable and low-maintenance
Clean with Windex to protect from PETG
Can be hard to source
Bare Borosilicate Glass
Printing PLA on bare glass can yield excellent results but requires your bed to be perfectly leveled/trammed and your z-height dialed in. I do not recommend printing PETG on bare glass as it can bond permanently and damage or destroy your glass. It's best to cover your glass with a secondary surface of some kind when printing PETG. I destroyed two pieces of boro before I figured that out.
Hair Spray/Glue Stick
These both provide increased bed adhesion for PLA as well as act as a release agent for PETG so it doesn't bond permanently to your glass.
You want a hairspray that includes a copolymer. Generally, any hairspray that has "extra hold" on the can will do but a lot of people have found good results with Aquanet brand. You'll want to spray it on a paper towel then wipe it onto your glass or at least take your glass away from your printer before you spray it. You don't want the hairspray gumming up your lead screws or sliding components.
For glue stick, Elmer's purple washable glue stick is cheap and effective. Using it is pretty self-explanatory. Cleans up best with just soap and water.
This is probably the best print surface for beginners as it's very forgiving and easy to apply. Just use the cheapest painter's tape you can find. Of course, the wider the better. After you apply it, wipe it with a paper towel and isopropyl alcohol to remove any residue.
More expensive and harder to apply than painter's tape but transfers heat much better. I get a spray bottle of water and keep my plate soaked when applying Kapton. Doing so allows you to reposition it and squeeze out any air bubbles as you lay it down. Again, a wider roll means you have to apply fewer strips but it can get quite expensive.
Hands down the best print surface. Smooth finish, high temperature resistance, and provides good bed adhesion when heated yet releases prints smoothly when cooled. Requires no surface prep, special solutions or tapes before each print. Clean with isopropyl alcohol before printing in PLA or with window cleaner before printing PETG.