Marissa, what do you expect a contractor to be able to bid *on* if you don't even have a property under consideration?
Even whatever you may consider to be a "standard" garage (or whatever) is going to vary widely in cost based on things like the specific lot conditions, and *all* remodeling is dependent upon the size and configuration of the building, at minimum. Time of year, weather, other demand, exact locations, the size of the firm, where it's located relative to your project, and more all go into a bid - and for an actual *bid*, you need to have all of the parts and pieces specified, for a specific property.
Otherwise, it will at best be an estimate, otherwise known in the trade as a WAG - a wild-*** guess.
Vary *any* of those parameters and you may as well toss the whole thing out. Which you'll have to do anyways, since an estimate given without any details specified and not even a jobsite is worth less than any paper it might be written on.
You are *begging* to be taken advantage of by not even recognizing this most fundamental concept, that there is no such thing as a "one size fits all" construction/renovation job, and that it is literally utterly and completely impossible to do what you are asking.
Since you have zero experience at all with remodeling or building, please ditch the idea of buying materials yourself. That will end up costing you much more in the end, when something fails, for example, and you don't have the power of history with the vendors (or contractors) to help you through it - and that is definitely *when*, not *if*.
Good contractors warrant both their work, and in the case of materials they purchase, they will access the manufacturer's warranty on your behalf should a part fail. If you buy the parts, though, they are very likely to not even warrant their work since they can't be certain what they are starting with, and that will go triple for someone such as yourself who doesn't know diddly about construction and quality materials.
You also do not have the first idea of what needs to be purchased, to be honest. Would you know all of the accessories that need to be bought in order to install even just a simple light fixture, tub and shower fittings, or a toilet?
I can tell you right now that you don't - and that they don't all come in the box with the pretty parts that you see once it's all installed.
You can certainly learn these things, but don't try to wing it without some instruction of some sort, for your own sake. Fortunately for you, there's a fabulous resource in the Bay Area, the Owner Builder Center in Berkeley, which teaches some terrific classes that help people learn how to do their own renovations. Even if you never lift a hammer yourself, you will benefit greatly from understanding the construction process and the sheer complexity of what you are undertaking so that you have a better idea of what any contractor you hire is talking about and what they are doing.