Do roasted almonds have similar calcium value to raw ones

I find roasting any nut simpler with a bit of glue, some egg white in addition to any flavouring. I use one egg white mixed with a bit of water per 2C of nuts. Toss in the egg white, then in the flavour (salt, sugar, honey, spice, etc.), and bake off at 300-350, depending on the size of nut (lower for larger nuts).

Discussion of the long-term health effects would be little more than speculation; however, there is a specific nutritional claim which can be tested, and has been tested in the commercial food-processing setting.

See: Formation of Lipid Oxidation and Isomerization Products during Processing of Nuts and Sesame Seeds:

The aim of the present study was to quantify some nutritional and safety quality parameter changes that take place in nuts (roasting) and sesame seeds (dehulling, roasting, milling, and sterilization) during processing.

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All these parameters were significantly affected by the different processing stages, especially by roasting and sterilization (tahina). Nut roasting and sesame heat treatment increased the primary (hydroperoxides) and secondary (aldehydic compounds) lipid oxidation products, with the p-anisidine value reaching 6−11.5 and thiobarbituric acid reactive substances 3−5 mg/kg (equiv of malondialdehyde) in the different end products. In addition, roasting led to the formation of CML (between 12.7 and 17.7 ng/mg) and tFAs (between 0.6 and 0.9 g/100 g) in nuts and tahina, which were absent in the raw material. Roasting parameters appear as the critical factor to control to limit the CML and tFA formation in the final product.

You'd have to read the whole study for a detailed analysis of how roasting affects the lipid oxidation products, which are the same products seen in rancid or overheated fats, but there is going to be some effect.

This is really more of an issue in a food plant because they use big machines designed to roast huge quantities of nuts (we're talking 200 kg/h for a low-end, $5000 gas-fired machine). The heat characteristics of one of these machines is going to be completely different from the comparatively slow roasting of a tiny quantity of nuts in a home oven, so don't panic.

To be any more specific, you'd have to specify the kind of nut. The oils from different nuts peroxidize at different temperatures; some unrefined nut oils start to smoke at around 160° C / 320° F (peanut/walnut), others go well into the 200° C / 400° F range (e.g. almonds). In any case, it's very rare that you'd actually be heating the nuts up to these temperatures unless you left them roasting too long, and they'd smell very burnt at that point.

Just don't eat hundreds of pounds of roasted nuts every month, and don't burn them when you roast them, and you'll be fine.