Well, what I've done is drawn the panels first, with a regular size, and considered carefully which ones would need two panels' width/height/both.
This occasionally leads to a weird layout, though, especially when I do a double-height one.

You mean like put a grid over the paper and then keep the lines that best fit my drawings?

Well, that would work.
Though I'm not quite so organised

Ah. Well most art programs, including the ones I'm using, support their own grids, so I'll try that. Thanks for the idea!

You're welcome!
I don't know how much help it'll be - I'm not exactly a professional at this
Still, should give you an idea of how much space you have before you start, yes?

Yes! Thank you very much! *huggles*

I know that problem pretty well, it took me ages to figure out I could draw speech bubbles after the text.

It's all based on how much impact we want to convey with each Panel.

Dunno if this will help you but this is what I do.

For full page graphic novel style, it's pretty important that you don't make stuff up as you go along. It's very much process that needs to be put into a layout before hand. So yea, make sure you have your chapter done and ready to work with.

Doing layout usually takes a few tries to get right. I try to aim for 30 - 32 pages for my comic chapters. So I quickly scribble up a page full of 'thumbnail' like images to use as a storyboard, and draw small rough panels (with the first word or words from sentences in them so I know what's going where) or body outlines (kinda like police chalk drawings) if the figure has an exceptionally dynamic pose that will interfere with panel placement or I just really want to remember to include because I like it.

When you're done you will rarely hit the mark your looking for, BUT you will have an entire rough (very rough) storyboard to work with, so you can go through it and make changes, expanding some panel pages to more that 1 page that you think my have a better effect if the panel work was larger, or shrinking certain panels down that you think don't need as much emphases as you originally gave them in your layout design.

After you get a complete chapter story board for your layout you can go onto doing your actual sketch drawings for the chapter, if the layout works how you like it, then go with it, if you feel that it doesn't look right and needs some adjusting then fix it. The biggest thing that may call out for a layout fix is if a word balloon ends up being bigger than you may have thought it would be, so adjust accordingly. After you get the rough sketch of your layout / characters and word balloons you're pretty much ready to go onto the none layout process.

the way i learned was to figure out the layout during scripting. you sort of write and overview for the story you wanna tell, then become more detailed, adding scenes dialogue and such. once you do that, you can mark your pages off according to where they seem to naturally break for you, then one step further by thinking of which part of the scene you want of a snapshot of keeping in mind you want some of them to frame your text, there you have your panel count.

i don't know what software you use for your art, but if you can do separate layers, then you can put down individual shapes for your panels, then modify them as you see fit. i also have a template for photoshop if you wanna use it...

As it comes to panels, I typically work with multiple square ones of the same size in sprite comic cases, and sorta just wing it otherwise ^^' worked so far

using digital programs do the art first, then crop if you have to to get the "camera eye" for the frame.

Manually, divide the page and learn to draw smaller:/

Wasted space or missing awesome details is less important to story. If you go all crazy it can be hard to read. As a general rule empty space can be quite forgiving provided you don't go to extremes. Just be sure to some background in, no matter how simple, and most people won't notice. In my experience the opposate problem happens, not leaving enough space for speach, sound effects and so on.

If in doubt, whip up a rough with stick figures. It doesn't matter if the proportions aren't exact when you do the final.

usually helps if you have the story written out who says what. and you piece around the intensity of the conversation.

like if the comic zooms onto one specific person you instead of making the rectangle box, you make a circle.

if its a scenic view described, you take 2 panels worth and draw the scene.

you know... kinda like how manga artists do it.

OOooor you could just do what some others do, which is 1 page a week comics with equal size panels (common lazy comics i say but easy)