Today I’ll be taking a closer look at diversified mining giant BHP Billiton, housebuilder Barratt Developments, and British Airways owner International Consolidated Airlines Group. Is this the perfect time to buy a slice of these three FTSE 100 firms, or should you stay well clear in times of uncertainty?

Dizzy valuation

Short-term investors in BHP Billiton (LSE: BLT) will have enjoyed watching the value of their shares soar from the depths of 580p in January to current levels at around 960p. They’ll be wondering whether it’s time to take profits and bank a healthy return, or hold on to their investment and hope for further upward movement. On the other hand, long-term investors who’ve witnessed the painful decline of the shares from highs of 2,631p in 2011 will be nowhere near as satisfied with this year’s rally.

In my opinion there will need to be a seismic shift in the supply/demand equation before anyone can say with confidence that the commodities crisis is finally over. If anything, this year’s rally means the Anglo-Australian miner looks even more expensive than ever at a dizzy 85 times forecast earnings for 2016. I feel the shares could be heading for a nasty correction.

Bargain builder?

The home construction sector has been hit hard by the UK’s decision to leave the European Union, and as one of the country’s leading housebuilders Barratt Developments (LSE: BDEV) hasn’t been immune. Shares in the FTSE 100 builder have tanked since the Brexit vote, as the housebuilding sector tries to come to terms with the outcome of the referendum.

But the UK is still facing a housing shortage, and although demand for housing may be subdued in the short term, I believe Mr Market may be overly pessimistic at the present time. Trading at just six times forecast earnings, and with a well-covered dividend yielding of over 7%, I think the shares could be a bargain waiting to be picked up by brave contrarians willing to go against the panicked herd.

British Airways heads south

The travel industry is another sector still reeling from the vote to leave the comfort of the EU, with airlines and travel companies nursing steep declines since the 23 June vote. Amongst them is International Consolidated Airlines Group (LSE: IAG), the owner of British Airways, Iberia and Aer Lingus. The airline group issued a statement on 24 June saying it doesn’t expect this year’s operating profit to increase as much as it did in 2015, although the Brexit vote shouldn’t have any material impact on the business over the long term.

However, the statement did little to stop the group’s shares from heading south along with the rest of the airline and travel industry. No doubt a weaker economy would hurt demand for travel, but with the shares trading on just four times forecast earnings for the next two years, and supporting an exceptional dividend yield of around 6% I can’t help but feel they’re oversold.

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Bilaal Mohamed has no position in any shares mentioned. The Motley Fool UK has no position in any of the shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.