First, remember that you can take out your contributions to a Roth IRA at any time, and you can take out up to $10K of earnings to buy your first home. That will provide a significant chunk of cash that you can use to buy a house, if you so choose.
Second, you have the benefit of knowing your target RE date with a degree of certainty most don't have. So take advantage of that to plan your investments over time to maximize your overall 'stache. Sounds like you want both a 'stache to supplement your pension (which you are going to want to grow to last another 50-60 years), and a chunk of accessible cash @16 years from now for one-time use on a house. So for the next 10-12 years, throw as much as you can at the Roth to build up your long-term 'stache -- the primary benefit of the Roth is that you get tax-free growth and withdrawals, which will help maximize your long-term 'stache, so you want to focus on that now so it has as many years as possible to grow and compound. Then, when you are maybe 5 years out, take a look at your overall situation and figure out how much accessible cash you need to buy the house you want. Divide that amount of money by the numbers of years you have left, and then each year put that amount into a regular taxable account instead of your Roth. Since that is short-term money, put it in something like a money-market or CDs; the fact that it's a taxable account won't hurt you much at tax-time, because you're not looking for growth from that account. Meanwhile, all the money you put in the Roth over the prior 10-15 years will continue to grow while you pile up your house fund.
Third, I second the notion that you may well not want to buy a house all in cash. But since you don't actually have to start saving for that for many years yet, you don't have to make that decision right now.
Finally, don't sweat the details now. You have many years to go, and it is very likely that your situation will change, your needs/desires will change, the tax laws will change, and the economy will change. So rather than trying to foresee the future, just save as much as you can now, using the approach that current information suggests will maximize your returns (that would be throwing everything you can at tax-sheltered options). Then, as things change, you can re-evaluate whether that approach still fits your goals and is still the best path to get you there.