Measuring wood sash windows for glass is pretty easy, you simply measure the wood indentation where the glass lays, the best way to do this is to beat out the old puddy with a pair of gloves a long sleeve shirt a small flat tip screw driver not too sharp and a small hammer, and then you measure, but of course you can measure with the old broken glass still in the frame you just have to spend alot of time doing a close inspection.
The puddy is at a forty five degree slant, so you measure from the top of that slant, where the puddy meets the wood to the opposite side, standard wood sash glass measurements are: 26 x 15, 26 x 21, 26 x 24, 32 x 15, 32 x 21, 32 x 24, even numbers are usually the standard sizes,
But of course there are the goof ball sizes which vary, sizes like 33 3/4 x 37 3/8 or 34 x 24 , houses built during the war had weared sizes and houses built during the depression had no regulations at all.
Here are some "learn ya's how to do it videos", we have found these videos to be quite useful for teaching people how to deal in the world of DIY or (do it yourself) DIY is a good thing because it enhances your ability to save lots of money, and money saved is money earned.
Patio door rollers are the little wheels that keep your patio door on track up and rolling. Don't let yourself get off track with square wheels. Learn how to clean and service your rollers just click on this link.
if your dealing with something that's to large for you to handle than by all means you need to call a professional.
Glass is dangerous and big glass is even more dangerous so don't try to do something that you cant handle, (36"x 60" is probably the biggest most people can handle without needing a truck) .
There's other video's here besides broken window video's, doing puddy jobs, installing rollers,etc. just click the video you want to learn and start learning.